The_Donald was (1) banned and (2) not the official politics forum. It's more like characterizing Reddit as a whole as left-leaning because /r/politics is, which is, in my book, a fair claim.
I mean the goofiness comes from "what are the politics of a website" being inherently kind of a strange question with no clear answer. The motivations and values of the people who run these sites are mostly not legible to us. We can look at what the sites are used for.
If someone is using their own money to host a forum for neo nazis it's very coherent to describe this behavior as, at the very least, supporting neo nazis. If they are also hosting a motorcycle forum with their money, does that cancel out the neo nazi support? Is it reasonable to say either site IS a nazi forum?
What if most but not all members of the motorcycle forum are also nazi forum members? What if only a few of them are? What if they share login systems and comment histories?
There aren't clear boundaries between these things. The nazi forum is definitely a nazi forum. Whether the motorcycle forum is a nazi forum depends on how much userbase and culture and branding they share, and how high your tolerance for nazis is; an individual assessment without an objective answer.
