A tankie is a leftist/communist who thinks "send in the tanks" is a valid and viable strategy for political disagreement (see tiananmen square)
A terf is a Trans-Exclusionary Radical Feminist, basically a transphobe who either is pretending to care about women's issues to hurt us, or has been traumatised by some past event and is taking it out on us
No, they like to claim they are communists, in the same way Hitler claimed to be a socialist, and the Kim family claim to be republicans for peoples' democracy.
I'm curious if you've followed the sources on that article. There's a few that are decent, but a good chunk of them are further articles and opinion pieces written by socdems and establishment liberals, which probably isn't the best thing for a trans instance that heavily pushes socialism, anarchism, and communism.
I don't know what sort of person could be an active Lemmy user, on the Blahaj instance no less, and not ever have encountered tankies or terfs. Frankly I'm jealous
It's probably worth saying that these days "Terf" tends to get used for anyone that's anti-trans, regardless if they are identifying as feminist or not.