How is this a brilliant?

Please help, I don't understand this.

You could have tried to save your knight maybe?

Wow

Black can try to save the knight (with Nc2), but the knight is trapped anyway, so it isn't any better.

When black leaves the knight to be captured, and plays a random legal move, the dumb chess.com script sees it as a "piece sacrifice" which is good (as there is nothing better, the knight is lost anyway). So it awards the "brilliant" title. Which doesn't make any sense.

maybe a pawn could have been gotten for the knight

I think that after Qxa1, you go pawn g5, Bg3 and pawn h5 and start an attack. If you play Nc2 to try and save the knight, it's trapped so there's no point in saving it. at least that's what I think.

It's not.

The game has really dumb standards for brilliant moves.

The best thing I can see here is that you can follow with g5, which will largely immobilize white's bishop and knight and allow you to castle away to safety. But that's a completely obvious move.