Well, you usually need a university address or some endorsers to post to the arxiv, but true, most people could probably post that.
On the other hand, the arxiv is also the default method of communication in quite a few fields (physics and maths, mostly), to the point that while grant committees etc. look at your peer-reviewed papers, I essentially only check the arxiv for new developments, not the plethora of properly peer-reviewed journals.
I looked over that paper, and honestly it is nothing that impressive. Basically it just described applying off-the-shelf algorithms to a particular kind of data. It probably would be published and is interesting to look over, so I don't mean to deride the paper itself, but still it is just not that novel. Nothing about how their end-to-end self driving works or how it's better than the many competitors. So to me this was hugely underwhelming, really.