It’s a fake guys. Don’t be so naive.
Fact-check

the real one isn’t better tbh (tl;dr: he originally tweeted that ‘cis’ and ‘cisgender’ are slurs, also many links are down because of his whole rate limit policy)

Literally any words could be made a slur dependent on how you use them. It's the ones that are near universally a slur, such as the N word, that anyone should care about.

The fact he didn't feel the need to censor cisgender would be enough to tell you on what level that "slur" actually is.