A company might switch from Github Enterprise to Gitea Enterprise if they were fed up with GitHub Support (or lack of it) and wanted to be able to run on-prem with k8s.

What you're not understanding is the way DNS works is the closest DNS server to you (usually your ISP unless you've configured it differently) usually caches the results and then serves those results for subsequent requests.

So you are relying upon the server that is caching those results to serve your data. The intent of DNS TXT records was not to provide you with a content distribution network for free.

How come no one is mentioning that the source of all this traffic was the downloading of an mp3 that the OP probably doesn't own rights to distribute?

I don't see how that's in any way relevant to the real story. It just as easily could've been a 3 MB photograph.

Does this mean the Seattle campus on Mercer Island is no longer opening?

It's opening in Q2. Source: I'm one of the subjects of the article :^)