Is this a checkmate for White? [FEN "8/3RkQ2/3B4/8/8/8/8/8 w - - 0 1"]



Is there a way out for Black?
 My son and I finished this way (only the relevant parts of the position are shown in the diagram), but reading about stalemates now has us confused. We are new to the game and I would appreciate an explanation.
This would be checkmate, because the king is in check and has no valid move to escape. But it's impossible to get into this position if you follow normal chess rules. The most you can do is a double-check (using a discovered attack), but your position shows a triple-check.

The stalemate rule is only applicable when the king is not in check, so it doesn't apply here.