I Walked In On My Son....

Advice please! My son just celebrated his 15th birthday and his best friend stayed the night. I got up around 10pm to use the bathroom and he left clothes on the floor again. I go to his room to tell him to pick up his clothes.... And him and his MALE friend are making out pretty much. We just stood there in shock staring at each other and I just walked away not knowing what to say. His best friend ended up calling his mom to get him because I guess he felt awkward. My son has been completely avoiding me the last couple days. I don't know what to say.... I feel there needs to be a talk but idk jow to go about it.

Edit: I want everyone to know I'm not homophobic. Yes I was surprised he was kissing a guy because he's had girlfriends in the past and has never given me and indication that he may like boys.