Anything that meets that definition is always FOMO. Anything that does not meet that definition cannot possibly be. FOMO is controlling when players are allowed to experience(/buy) content in order to force them to play when you want them to. Any intentional time limited window is absolutely always FOMO.
Until it's gone again. It does come back but you could miss out till then. Hence "fear of missing out". I feel like you're purposefully ignoring that it is FOMO.
These are false equivalencies. Why not make them available all the time? Have you ever asked why they don't? Because them going away for an unknown time drives purchases. Now why does it drive purchases? Because people are afraid of missing it. You can get it eventually sure, your just punished for not getting it then and have to wait. It's textbook FOMO marketing, saying it's not is just silly.