Then again, you can also just look it over...not necessarily ignore it, but just feel comforted enough that you know...and he knows that you know whether he's willing to admit it or not.
Take his lack of confidence in admitting it as mere shyness or being uncomfortable with it.
You shouldn't need him to verbally admit to it to feel okay about it. He's uncomfortable with being open about it just like you're uncomfortable with watching it yourself.
It's just p 0 r n...it's really not that big of a deal. I don't think you should put too much thought into it. If you do, then he's going to think you will turn every little thing into a big deal and start hiding more from you just so that he doesn't have to deal with you "bitching" about it.
I'm not saying you're bitching about it, but men have a tendency to think that women are always bitching when they're not saying something extremely positive.