The fact is that there are no scenes in Prince of Thorns where someone is tortured. Possibly you could call it torture innuendo as the subject was definitely mentioned. But, if he had read on (which he didn't) he would have found a rather upsetting scene with a dog in the second book, and had the third book been published when he made his comment (it wasn't) then yes, there was an actual torture scene in Emperor of Thorns.
So the real question is not whether the trilogy as a whole contained torture (which is nothing new - one of my earliest fantasy reads, Moorcock's The Knight Of The Swords (1971) practically starts with the protagonist being tied down and having a hand chopped off and an eye put out), the question is whether it was torture porn.
Porn, as they say, is hard to define but we know it when we see it.
We could just say 'gratuitous' instead, but that's only shifting the furniture around. Who's to say when something is gratuitous. Is the ubiquitous fighting in fantasy books gratuitous? Well, no, it's generally the most likely solution to various disagreements. If the protagonist went to the library and challenged the librarian to single combat in order to take a book out, that would be gratuitous.
So, when is torture gratuitous? You could say that it is not gratuitous when there's a valid reason for it happening. If a cruel enemy got hold of a hated foe then they might realistically torture them before killing them. And thus a book could be as full of torture as it was of swordplay and might be argued not to be torture porn.
However, torture, like porn and a select number of other subjects, do not get an easy pass like this. For them the question shifts its ground and says not only would it happen but do we need to see it? We don't ask if we need to see the sword fight or be told mechanical details of the cuts and thrusts. But we do ask if we need to see beyond the bedroom / torture chamber door when it closes and be told mechanical detail of the thrusts (porn) and cuts (torture). Society has set a higher bar when it comes to these subjects. We have either to admit to a close interest in sex, or in torture's case we have to justify its inclusion in some other way since I will readily agree that whilst a close interest in sex is generally quite healthy, a close interest in pain is … less so.
The question has narrowed down to: was there a good reason you showed us that?
And for the times that I've written a torture scene (which depending on how you count could number as low as 1 and as high as 4) the answer has been yes, there was a good reason. First let's side step into "shock value" for a moment. I've blogged on shock value before, and although the phrase is offered as an oxymoron, I disagree with the notion that it is one. However, I won't focus on the fact that shock is actually valuable here. The times that I have written a torture scene there were good reasons (other than shock value) to include them. Specifically: I write character driven, character focused books. I generally only have one main point of view character per trilogy. I generally have that character grow up across the course of the books. Coming to terms with the real evils that are out there - which may involve encountering them - is a genuine and formative part of many lives. It's one thing to have monstrous adversaries but the "the real monsters are us" cliché is a cliché for a good reason, it's focused on a lot because coming to terms with the things we really do to each other is a big deal, a big part of the human condition. How we react to the challenge that such knowledge poses to our world view, our security and psyche, are key moments in deciding what kind of person we'll be. Yes in a drama of manners set in the 18th century we can present these challenges to a character in a more genteel way, but in a harsh fantasy world with medieval vibes … other paths can be taken.
In Jorg's case, he is a youth who has from an early age armoured himself in a very goal-focused, self-centred personality, viewing others as a commodity to be spent. This personality is one that he has either chosen or had thrust upon him as the best way to insulate himself from the horrors of his childhood and to ensure he will never again be so vulnerable. In Emperor of Thorns his very close encounter with the sharp end of the instruments of torture is one of a small number of major blows that begin to crack the shell of not caring that he's built around himself. It forces him to re-examine himself from a new perspective. He doesn't have an instant epiphany, but it's part of a his growth process, that carries him from who we see on page 1 of book 1, to who we see on the last page of book 3.
To conclude - torture porn is hard to define, but I know it when I see it (I'm looking at you Saw), and I don't see it when I look at what I've written.