alt Hacker NewsCan't directly answer your questions, but generally each region/time period has their own style of arrowheads, so my assumption here would be that this region tends to create arrowheads in this style. The paper mentions this is a pretty old site/artifacts, so I'd wager they found other "arrowheads".
Arrowhead might also be being used generically here to mean sharpened stone tip on a projectile or thrown weapon.
I'm no expert in this area, but it may just be that we aren't sure if these are arrowheads or just sharpened stones that were put on something. Someone correct me if I'm being ignorant. The article really makes it seem like a lot is unknown here, since we're dealing with 60,000 years.
There are a number of ways they're able to tell the difference between arrowheads and sharpened stones put on a stick, including high-resolution CT to look at the stress microcracks of the arrowhead. Bow-fired arrows and thrown spearheads have different launch stress profiles as well as impact profiles. There are a lot of overlapping types of analysis that happen to establish what technology did or did not exist in a given area at a given time.