The core of your argument is that you don't think many reloads, by different users, from different Tor IP's, is convincing evidence, and I think that makes you part of a very tiny minority.
I had the same result, 8 connects from "new identity" feature, all ips blocked. It may be temporary though, but today, for sure they are blocking tor.
I don't know StackOverflow's Tor practices. Given the post's title, I was disappointed to finish reading the post and still not know. If I had read the same post with a title like "Ask HN: is Stack Exchange (Stack Overflow) now blocking Tor?" I would have no complaint.