In actuality, Gab bans users for the same reason Twitter does. For instance, when Paul Nehlen tried to organize harassment of another white nationalist figure, Gab banned him. Part of Gab's sales pitch is that it's a refuge for people whose thoughts are somehow too dangerous for Twitter. But contrary to what Gab wants you to believe, Twitter doesn't ban white nationalists. Richard Spencer has a Twitter account. So does Faith Goldy. For that matter, so does Gab, which has posted openly anti-Semitic comments in the past, and still has a verified checkmark!

Gab also banned people who posted anime porn, sending them in flocks to ActivityPub instances.

The users Gab banned were already on such instances by and large, in particular smuglo.li and pawoo.net.

Faith Goldy is not a white nationalist

Faith Goldy literally said the 14 words and claimed they weren't controversial in a recording.

If we aren't putting her in the white nationalist classification I'm not sure who does end up there.

     How is a platform that let's you say anything uncensored intolerant? 

That's another way to say "a platform that tolerates the intolerant" which could hardly be a better example of what Popper is talking about.

That said, the OP is also not right to suggest that intolerance is simple to identify. Like the other comments here say, it's subjective.

Then again, most things in life are subjective. Society has to be pragmatic sometimes and ignore that. Otherwise everything, eg: the legal system, falls apart.

When Popper described intolerance, he spoke of people using 'fists or pistols' to shut down the tolerant and he predicated the very idea on the right to self defense.

The right of self defense is and long has been defense against immanent physical harm, for the one who does not start the fight.