Anti-fa stands for anti-fascist, which is already not the same as anarchist. There are authoritarians who are anti-fascist. (Fascism is a particular subset of authoritarianism.) The way it's used today, anti-fa/antifa is a word for demonstrators/protesters who don't have a single organization/leader for others to negotiate with. They could as well be called The Unaffiliated Anti-racists. Anti-fa also refers to a tendency of action from Europe (mainly Germany, i think?), that emphasizes street fights and immediate physical reaction to nazi and white supremacist activity.
So, antifa gets used to refer to people who are prepared to destroy property and actively defend themselves and/or hurt racists and fascists.
And Antifa these days is also a group of people who believe that that kind of destruction and defense can make a significant impact on racism and fascism as larger social problems.
Some people in those above groups are also anarchists. Some anarchists are not those folks. Anarchist are against racism and by definition are against fascism, but not all anarchists think that street action is the best tactic, or that fist fights against racists are particularly significant in making fundamental change. Some anarchists think that obviously racism and fascism (etc) are crucial issues, but that street fights are frequently a distraction from the systemic problems that are harder to see and a lot harder to fight.
edit: why so much confusion?
1. elected politicians who are inarticulate and/or intentionally blur definitions as a way a) to scare people with mysterious, dangerous, amorphous enemies, b) to be more difficult to refute (if they're unclear and muddy in their language, then they can pretend that listeners are confused or dumb, instead of the politicians being confusing and mystifying).
2. anarchists/activists who want to appeal as broadly as possible so that they gain power/bodies (appeal to the lowest common denominator--as the vast majority of people are anti fascism), "all these people agree with us, so you should listen to what we say"
3. anarchists who have never been clear on what is actually radical/challenging about anarchism, mostly see it as the most radical flavor at the moment, until the next trend comes along. fighting fascism and racism are the thing of the moment, so anarchists will do that now, because anarchists are the most xtreme...
off the top of my head, anyway...