Teams Checkmate

https://www.chess.com/4-player-chess?g=11283252-19

This is a checkmate and I knew it was going to be a checkmate in the game but after thinking it through I don't think it has to be a checkmate. I am assuming I am missing something though. What am I missing?

If Green's queen proceeds to take the Red queen (Qxm7), then red moves (Bxm7 maybe?) and then Blue takes the yellow queen (Qxm8), no kings will have died. Right? Does this have to be a checkmate?

If it's the side being checked's move then it is mate...

You can't move anywhere

Right. On any given turn, a player must be able to move out of check. While Green and Blue could technically avoid the Green king getting captured if gameplay continued, the reason it is checkmate is because Green is in check and has no ability to get out of check. Taking the red queen still leaves Green in check.

Thank you for the clarification. All clear. Much appreciated.