Since Forgotten Histroy incorporated so much from TAS, does that mean we consider all things from TAS as having happened?
I don't think so. Heck, there are parts of other series' canon that I don't consider to have happened, and that nobody else seems to either since they've been contradicted in later productions, like "The Alternative Factor"'s portrayal of antimatter, or ST V's portrayal of the center of the galaxy as easily reachable, or the entirety of "Threshold."
Canon is not some exhaustive mandate. Canon is simply the pretense that a bunch of different made-up stories represent a coherent reality. But any canon has mistakes or bits that don't quite work and that get ignored or retconned away later on. Since it's all just pretending to be real in the first place, it can equally well pretend that parts of it never happened.
While TAS is a pretty solid series overall, there are a number of episodes that just don't make any sense or that are inconsistent with what was established later (or earlier; I don't see any way to reconcile Stavos Keniclius and his backstory with Trek history as it had been established in TOS, let alone in subsequent series). Personally I only count about 2/3 of it as "real."