Hunting rather than scavenging seems to be just an assumption, not investigated. But that's reasonable, they'd surely hunt a delicious giant sloth, why not.
I'd wager we would do both, but a limiting factor is need. A single giant ancient beast could provide literally thousands of pounds of meat. That's feeding a village for a very long time. And taking down one of these beasts, even with reasonably advanced technology would always entail major risk. Even now a days with advanced rifles/ammo, elephant poachers are sometimes killed by elephants. And finally it's not just killing it, but then processing/preserving the meat, and bringing it all home. That would have been a tremendous amount of work.
And nobody really knows how many humans were alive e.g. 10,000 years ago, other than - probably not many. There were almost certainly less than a million humans in the entirety of South America. The max population density there would have been 1 human per 18 square km. But of course in practice we would have huddled around water sources and in small settlements, greatly reducing our overall spread. So you could probably have traveled hundreds of kms in all directions before seeing a single human. That's just not a lot of people to completely eliminate a bunch of massive species throughout an entire continent.
By contrast these species all started disappearing just about the time when we were leaving an ice age. And these animals may have been overadapted not only to the cold, but the associated vegetation/prey and feeding patterns.
https://www.science.org/doi/10.1126/sciadv.adx2615
Hunting rather than scavenging seems to be just an assumption, not investigated. But that's reasonable, they'd surely hunt a delicious giant sloth, why not.