Earlier quoted context omitted.
They’re different concepts, and disassociating with alt-right conspiracy nutcases is unrelated to free speech.
Banning alt-right conspiracy theory nutcases might just be related to free speech, however. And that's what most people seem to want Gab to do.
Choosing to disassociate from speech you don't like is yet another use of free speech, as is banning groups that use speech you don't like from your private platform.
So yeah, gab, Reddit, and Facebook are exercising their right to free speech.