I think you’ve misunderstood the article. The FOSS didn’t sell out. It seems that Varnish (as an open source project) was created/sponsored by a company who later took the name “Varnish Software”. It was sponsored by a company but not bought and we wouldn’t have had Varnish at all if not for that sponsorship (to literally create the software in the first place).

They admit they should have gotten a firm agreement about their use of the name but it wasn’t a FOSS selling out and handing over power.

And I also understand why Varnish Software might not want the IP rights just in case the bot get mixed up. I actually think departing and with a new name is perhaps the best outcome.