Yes, of course it's totally fine for people to post their excitement about something like that. It may be a tangent, but it's a specific, interesting tangent, not the generic kind of off-topic discussion which is predictable. Also, there's a huge difference between a community member sharing excitement with fellow users vs. someone showing up just to promote something.

But note that OoTheNigerian's comment eventually became upvoted (hugely upvoted in fact). That community correction often happens when comments are unfairly downvoted—but it takes a little while.