I believe you. I just suspect stockfish was misconfigured, it wasn’t playing at its highest skill level or something similar was going on. That seems more likely. (I’d love to know for sure though).

An extraordinary claim without any proof. Surely you believe the moon to be made of cheese, since we can‘t travel there to verify it‘s not?

Yeah his claim is quite absurd really. If it was a weaker stockfish (bad hardware, older version etc.) then maybe. Modern stockfish pretty much crushes any and everyone. A draw alone would be extremely impressive, and maybe doable with enough luck from a top player. But even that is very far fetched nowadays. Let alone actually winning.

Elsewhere in the thread he revealed that he achieved these results around the year 2015, which means we was playing against Stockfish 6 or earlier, estimated to have about 400 less ELO than today's Stockfish 18. Stockfish 6 didn't even have NNUE, so the real issue seems to be that he thinks his results from 2015 hold any relevance to the chess engines of today.

Quick search shows elo of stockfish 6=3278 (1 cpu).

To assume that a human can beat that is just delusional.

No not at all! You can find plenty of videos on YouTube of humans taking down 2015-era stockfish. Usually it involves exploiting specific weaknesses in the engine, for example bringing the game to a stalled position where the game nearly reaches the 50 move rule, and then the engine makes a disadvantaged move to avoid a draw.

Especially pre-NNUE, chess engines were often not fully well-rounded, and therefore a human with specific knowledge of the chess engine's weaknesses could take it down with enough attempts.