2) It's possible to inspire your followers to threaten people without making a threat yourself. Yiannopoulos has painted groups he dislikes (feminists, Muslims, etc.) as threatening and dangerous to his followers, which is a tacit justification of violence and threats against them.
#2 Very tenuous justification there. One that twitter certainly doesn't hold other groups to.
His followers have threatened some horrific stuff to lots of people, especially during the height of GamerGate harassment. It has to do with Yiannopoulos only if he intended to create those reactions among his followers, which I (and others) suspect he did. We'll never know for sure.
> #2 Very tenuous justification there. One that twitter certainly doesn't hold other groups to.
Agreed. Perhaps Yiannopoulos has grounds to sue Twitter for unfair treatment. I doubt it, though IANAL.
In this case, Twitter may not be using "inciting followers to make threats using dog-whistle rhetoric" as a criterion for banning people. It would ban Yiannopoulos and not, say, a black nationalist for one simple reason: Yiannopoulos was more famous and created more consternation among potential users.