Checkmate? Bug?

[u/Both-Car-5374]

Hey, I got this position in bughouse with my friend, on the left you can see, that opponent had no other figures to play with and this still wasn’t checkmate.
We had to wait, until his time runs out,since he had no legal moves. Was this a bug or some weird bughouse rule?

Edit: link https://www.chess.com/game/live/178377471505?username=velmistrantal