And it's certainly not "far left". Being against Nazis and other Fascists seems like a pretty middle of the road idea.
Antifa today is still pretty firmly focused on anti-fascist action.
I'm not a historian, but understanding is that there isn't real continuity between that antifa (labor and communist anti-Nazi groups) and the modern antifa (the punk-direct-action-aesthetic antifa), which came about much later in the century, but that the name and association was adopted intentionally.