Tankie is a pejorative label generally applied to authoritarian communists, especially those who support acts of repression by such regimes or their allies. More specifically, the term has been applied to those who express support for one-party Marxist–Leninist socialist republics, whether contemporary or historical.
Some folk identify the .ml (or the pronouns of hexbear users) and work backwards from there.
Simply: the bad faith was having .ml there in the name. I'll take him for his word and bet that's what was meant.
*edit
And it isn't like I haven't seen wingnuts go ".world eh? More like .nazi!" as well. It is just that whole general vibe with the people who all up and comment about blocking shit.