In Steven Universe Future when Garnet said "My bad, I was sure we were in the pepperoni timeline." it put me off. Garnet always knows whats going on. Its what played into her "mysterious" character act. She always knew the right thing to say and do because she can quite litterally predict the future. For the show to say that she got the timelines confused in a throwaway line when she'd always known what to do, was strange but easy enough to shrug off. After all theres no threat, no reason to keep track of the future. Its reasonable she can get confused.
Until I realized this isnt the first time its happened.
In Pool Hopping Episode 15 of Season 5 Garnet says this "Sorry I must be thinking of a different timeline," after saying Vidalia must be upset her son went into space when it was in fact Lars that went into space.
This is the only time in the entirety of Steven Universe that Garnet mixes the timelines up. And here it clearly isnt cause theres no threat. We're reaching the climax of the show, theres very much a threat. There is only one similarity between the two events.
Garnet cannot predict Steven. She realizes in Pool Hopping that the reason her timelines are mixed up is because she has been looking into futures where Steven behaves as he did before and not as he does now. Once she corrects herself, she can once again guide their path.
In Future she is doing the same thing. Seeing Steven as he was before and not as he is now. Its why every single thing she does in future is wrong. She gets him a backpack with everything he needs only for him to evidently prove he does not need it. She prepares a dinner and games he should enjoy only for him to storm off to his room. She gives a comforting statement and it just annoys him.
Garnet does not predict futures incorrectly. She always knows what will happen. She just has to know what futures to look for. And considering the amount of shock and horror at the revelations of everything Steven has been up to, we can clearly see she has not been seeing the right timeline and had no clue this would happen.
I dunno i just think its cool that you can unpack all this in a throwaway line she makes.