I agree, which is why I consider this argument, that atheists are really theists, who are just angry with a deity, to be irrational.
It contradicts the commonly understood definition of the word atheist, to insist they’re really theists. That strikes me as a No True Scotsman fallacy.
X Atheism
Y Theism
Y can’t believe X really disbelieve, so an argument from incredulity fallacy.
Therefore Y assumes X are really Y, and offers a premise that would rule out X. So a No True Scotsman fallacy.