There are some questionable things that happen in that duel, but a lot of it is surprisingly OK for Polish cross-cutting saber. And remember, at some point the short guy is toying with the increasingly desperate prisoner.
And martial validity isn’t everything in an on-screen duel. There’s a ton of martially absurd stuff that happens in Westley vs. Inigo, but it’s still one of the best on-screen duels ever.