WHY DID HE DO THAT

So there’s this guy I always hang out with (I’m a virgin so no sex) all we do is cuddle and just go places so his sister was in town and we were at his house and he all of a sudden disappears and doesn’t tell me where he’s going so while I was wondering where he was I decided to put on a charcoal face mask and I’m just sitting on his bed on my phone waiting for it to dry and next thing you know I hear his older sister come up the stairs and she greets like normal??? I was in shock and embarrassed and then we just started talking about him and other things SO my question is, did they plan this out??? I have literally never dated anyone nor had sex so I’m clueless about these things... (he’s 28 I’m 22) lol