Is it a bug, or did I screw up something

So yesterday, I got a rade invitation from a friend. I am quite new to the game, but I know what that is, so I accepted. Then I joined the lobby, and chose my team, while doing that I could see him and an other dude. (You know standing next to each other, like we were in the same lobby) When I joined the raid itself, like the fight, I was alone, and I don’t get why because I could see them even if I like went back to the pokemon chose screen, but I was fighting the raid boss alone. Did I mess up something, or what happened wrong?

They probably left the lobby bc there weren’t enough people to beat the raid
So they didn’t waste their pass

The Raid System is quite buggy at the moment, so it may be a bug.