Should I be annoyed at my boyfriend?

Ok so basically I'm only 15 and my boyfriend went away on a trip with his school for athletics to Portugal and is sharing a room with two other guys. Me and alot of my guy friends are in this chat and the third guy in the room posted that the other two were wanking together to my boyfriends porn. Now even though I think that's messed up its the porn that I'm angry about. I get that all guys watch porn so I'm not angry about that it's just when I asked him "did you really do that?" He messaged me back saying "well it was my porn and I was horny, who wouldn't if there was good porn"

No I personally don't think you should make excuses to your girlfriend by saying "sorry there were other hot naked ladies how could I not get hard" (which is virtually what he was saying)

Do you think I should be angry about his message? Is group wanking normal for boys? Am I just not being reasonable? Please someone help