The issue wasn't the anti-trans rant; Valve specifically called out the fact that the patch notes included personal attacks.
For better or worse, Valve is intentionally very lax when it comes to censorship (they ban illegal content and trolling, and that's about it):
https://www.polygon.com/2018/6/6/17435324/valve-steam-policy...
For the heck of it, and to confirm nothing has changed, I looked and took me about 10 seconds to find some trans-phobic stuff they host.
Good on valve for putting good community first.
Wouldn't a blog post or a social media post be a more appropriate place for something like that, given the larger focus on interaction and outreach on those, versus something that is generally (in my experience) just used to list a bunch of changes between two versions of software?
That said, I agree with Valve that there really shouldn't be a place for harassment or really toxic behavior on the platform, at least when it's possible to limit it. Interpretations of what counts and what doesn't might vary, but this seems like a decent example of moderation action.