chess.com secret draw rules?

Context: this is my brother and me goofing around. I wanted to see if I could promote all of my pawns to knights without stalemating to even out our discrepancy, since we have a constant game going (and I’ve won the last few). He was down with it.

There was a valid move for the king, but chess.com called “draw by agreement” the moment I promoted my third pawn. Is this a bug… or does chess.com have additional rules they’ve added to the game? Am I missing something here, or some obscure rule I don’t know? I’m more curious, than anything, as this really wouldn’t come up in any other game for me. Thanks!

https://www.chess.com/daily/game/642668053

Update: my brother let me know he offered a draw as a joke. I believe there may be a bug in the iOS app, because I “accepted” the draw the moment I chose “OK” on which piece I chose to promote to, without ever seeing the draw message. Is it possible that the “OK” button somehow gave a “Yes” event to both the promotion and the draw request?

Yes, possibly