That's such an extreme claim. It defies common sense. You'd have to proclaim that there was some event that _stopped_ evolution in humans, universally. How is that even possible? Especially 50k years ago. I'd be a little more forgiving if the claim was that evolution stopped in, say, 1999.
Sounds like they just meant evolution takes longer than that?
To some degree it's true. We have all sorts of variable parameters that are probably different from back then (eg. Average height) but we still have the same body shape, etc
Emphasis should be placed on "everything we call culture and civilization". There is a thought experiment that might help. Imagine we had a time machine, and no scruples, and we could go back and pluck babies from the past to experimentally raise them in modern American families. I'm pretty sure Gould would have argued that babies from 40k years ago would grow up to be behaviourally indistinguishable from modern humans.
Rather a lot more things about human genomic history are known today compared to 2000.
Discoveries about being able to process lactose and when those genes evolved all were after 2000, for example.
Does it excuse Gould for making such bold claims? You have to decide I guess. That is a lot fuzzier.