[bug/cheating computer] You can't propose draw, but when AI blunders rook...it ends game as draw !?

Here's the game (from position):

lichess.org/GgDENdIP/

I think that for the most of time it was the draw, as I noticed that I can hold out against the black rook, while the pawns are blocking the king.

So, as I couldn't find a way for black to proceed against me, while I was completely bound too, I decided to propose the draw. However... the option was unavailable for some reason?

I don't know why, is it because computer was winning, thus I couldn't ask for a draw?

Anyway, I kept repeating my movements, hoping for 3-fold repetition, when AI suddenly... blundered a Rook!!

It was an absolute win for me now, as I had big pawn advantage! So, I proceed to capture the rook, but then... I noticed that I can't? Because... the game ended in draw!? :O

WHY?

I didn't offered the draw, as there was no such option, and the AI didn't asked me for a draw too.
There was no 50-rule in play, as the game would ended earlier - we made about 56 moves from the last capture and there wasn't even a check in the whole game.

Also, if there was some other rule in play, to finish completely drawn positions, then the game should just end as draw, right?

*****

So, to sum it up:

The AI just blundered a rook, but instead of allowing me to capture it and win the game... the match ended as a Draw, for no reason, I suppose?

*****

Anyone have an explanation for what just happened? :O

It is 50 moves rule. If in 50 moves there is no capture nor pawn move, it is a draw. Computer moved pawn in his 7th move. "Blundering" a rook was 50th move.

Turns out, that Stockfish has sense of humour :)

Ahh, so it's like an "irreversible" move?

Thank you! I missed this one, looks like I remembered the different definition of 50-moves, i.e. without moving of a pawn, just captures.

Looks like I need to read the full FIDE rules properly. Thanks for explaining.

Lichess AI doesn't know how to respond to a draw offer.