> "Ardelean says [...] “I definitely advocate for the
> idea of lost groups,...”

Since he lost everything (teeth, hair, DNA, identifiable people, and where they came from and how), is there any other possibilities besides a lost group of woolly capuchins?

> I think it's being rumoured that perhaps the artefacts might be the work of capuchin monkeys, or similar.

"or similar" maybe even better.
[en.wikipedia.org]
But are they smart enough to make stone tools?
[www.mensjournal.com]
How they got to North America is easily explained:
[www.bbc.com]
If alien-invasive-marine species can get across by tsunami, I see no reason a mammal that eats almost anything and with a large enough raft of drifting debris shouldn't have any problem getting to North America. From the coast it was just a matter of heading south to Mexico looking for a Pleistocene site high enough above sea level to make snowballs and crude stone tools. Not impossible, but not very probable either.