I was curious to ask, why is the ending that is usually called the "bad ending", called "true ending" on speedruns? I might just be missing information about the game, so thank you in advance for any answer.

True ending is gotten. You get the true ending credits and final cutscenes but do not have to fight nyx or climb Tartarus by using a glitch to skip Nyx that involves talking to Tanaka on a specific day (FES only). Older runs didn't use this skip just because it wasn't known by the runners at the time.

oooh I see, completely makes sense. thank you!