Antitheism is not about knowledge or belief. Its literally in the name, to be against theism. One can be a believer and still be against a religion for all the harm it causes.

Agnosticism is the belief that it is impossible to know if there is a god

Atheism is the lack of belief that there is a god

Some atheists might assert that they know there is no god, but that is not the meaning of atheism, though some people call that "strong atheism"

On the flip side, one can be agnostic and think there is a god.

Being both atheist and agnostic (what some people call weak atheism) is the rational position given that there is no evidence for any god (or other supernatural phenomenon) existing, but that you also can't design an experiment that the result of would let you conclude a god (or other supernatural phenomenon) does not exist.

Occam's razor doesn't have anything to do with it. It is simply irrational to leap to believing things for which there is no evidence.

I mean, much like agnosticism is derived from "not knowledge", "atheism" is derived from "not god". "Lack of belief (in a diety)" is the definition of atheism.
The distinction between strong and weak, sometimes called "positive" and "negative", is "belief that there is not" vs "no belief that there is". Similar to how different strengths of agnosticism express "do not know" vs "cannot know". They both lack a belief in a god. An agnostic who does not believe is a type of atheist. Since they're compatible philosophies there's no contradiction or need to choose. Like liking chocolate ice cream and liking root beer.

they're just categories people made up, in my opinion, for the sake of arguing

First time talking philosophy? ;)

In serious talk though, I think your comment is a perfect example of why they are real categories. You have firm opinions on all of them, and all of them are actual things that people have believed and do believe.

Most of the "can't know" school of agnostics aren't "can't know therefore equal odds", but closer to "the question cannot even be rationally considered, so any opinion at all is irrational".
What color was space before the big bang? If you say it was purple, I would disagree with you. If you say it's not purple I would also disagree. It's beyond just a simple agreement about a set of facts, it's a disbelief in the existence of that set of facts in the first place.

What are you confused about in particular?

Atheism makes no claims or beliefs

It depends on your definition of atheist, I mean the picture is right there and right above it is someone explaining the concept further, I don't know what you gained from vomiting out something directly addressed in my own post and right above it

Atheism makes no claims or beliefs. Atheism simply says that claims made without evidence can be dismissed without consideration.

You're thinking empiricism. Atheism is most fundamentally the belief that there is not a god. There are atheist positions that are consistent with empiricism, but not all of them are, nor do they need to be.
There are gradients to it, but atheism is fundamentally about belief. The rational for that belief is a different set of philosophy.

Not cool. I am that which I am, and chose not to say what that is

If you do not believe in a god, you are an atheist, I'm sorry that offends you but that is literally the definition

This is like telling a Jew they're a Christian because the old testament is heavily cribbed from Jewish texts.

Not quite. It's like telling someone who says they're Jewish, that Christ was the true savior and son of God, and that he brought a new covenant that comes before the covenant formed with moses that they're describing Christianity.

That's exaggerating the point, but my meaning is that while your beliefs are your's and it's rude to correct someone on them, the word used to describe those beliefs can be much more readily discussed.