I believe this.
Joss Whedon I think is a genius. He has an amazing body of work and is fantastic writer and director. I'd go as far as to name him one of the greatest storytellers of the entire 21st century.
That said he is by many accounts a very difficult man. His treatment of Charisma Carpenter was absolutely shameful, Sarah Michelle Gellar appreared to have a very difficult relationship with him. She respected him sure, but there seems to be some bad blood there. James Marsters meanwhile has also not exactly made him out to be a great guy that he loved working with.
He's never outright attacked him, but still from what James says about the way he run the show, being scared of him etc, Joss seemed to be quite a bad boss. Amber Benson also didn't seem to be to fond of Joss either. The way Joss told Amber she was more or less fired, was pretty awful.
This is before we get to his smearing video games as sexists for petty reasons (they kill female characters, yeah because female characters should never be killd off. Also it's not like you've done that Joss?) Associating with charlatans like Anita Sarkeesian, all the while cheating on his wife!
I can believe that he was a dick on Justice League, but that said, does it matter? It makes no difference to my enjoyment of his work. Also I do think this actor is using the current political climate to settle an old score.
That seems to be happening a lot in the current outrage, and hey I love seeing phoney virtue signallers exposed for what they really are, but we need to watch this doesn't just become a witch hunt against people we don't like. I don't think Joss is racist at all. A difficult man, but not racist and he shouldn't be lumped in with genuine racists.