Because it kind of is when we're talking about an electric car. Tesla's competitors can't come up with those numbers for EVs combined (even with hybrids). GM is expected to make 30,000 Bolts for next year, for instance (and it may or may not sell all of them).
That said, I'm skeptical the Autopilot 2.0 hardware is a "Level 5 autonomous system". I think a good rule of thumb would be to subtract about "one level" from what Musk promises, as he always tends to be a little overoptimistic, even if what he creates still ends up being better than the competition.
Take the first Autopilot, which Musk said is "Level 2". It's probably more like a real Level 1. It only works under very specific situations, and even when those specific situations are met (a highway) it can still fail, because Tesla may have accounted for US highways but not European ones, or other road quirks. See the recent Autobahn accident because the Autopilot couldn't properly identify "yellow lines" as opposed to white ones.
So yeah, I expect this to be more like Level 4 ... three years from now (as ready for mainstream use, not just a demo). I don't think we'll see true Level 5 until the 2020s. I think there are still many unexpected things Musk and his engineers aren't foreseeing right now.