Actually if anything, it implies the Inquisitor had experience as opposed to Cullen. She's the one with the confident bravado, not him. She went in that room with one thing on her mind, judging from the dialogue options. They all make hints about going to bed or taking a break after a long day. She was the one who was inching closer and closer to the desk and eventually sat on it, basically not giving Cullen any option but to get on the desk with her. At least, that's how I remember it.
Also, don't forget that Cullen had unique trauma in his life, specifically about love (most likely). That's the main reason I don't think he was with anyone, at least not after the Fereldan Circle.
We can agree to disagree, because the way I saw it, it was Cullen who inched towards her, and proceeded to shove the stuff off his desk and crawl on top of her. If IQ strictly wanted to be the hunter, I would imagine it happening differently (i.e. her cornering him to his desk, or pulling him into her while leaning on the desk, instead of playing innocent and letting herself be cornered by him)
If those nightmares traumatized him about sex, enough to push him to total abstinence, then it really should've been addressed, that's really serious. That's like a video game allowing you to have a physical romance with a character who was a traumatized rape victim and it doesn't come up at all. Same thing if it traumatized him about love too (b/c love and sex aren't exclusive to each other) then that should have been mentioned, too. What the game does address in regards to his experience, is his trust of mages and belief in the Templar Order's purpose. In my eyes there's evidence in the game for me to see him as a dork helpless in courtship, but also someone who is not a stranger to being sexually forward and fluent (like that first kiss!)
I can totally understand it as legitimate headcanon to think that Kinloch left him apprehensive about love and/or sex, enough to be a virgin. I can totally imagine it being drawn out in a well written fan fiction or something like that, but from the game itself that just isn't how I see it.