Technically, you're all three right. It depends on the definition of
protagonist you're using. SenPC is using the original, traditional definition (what we originally got from Greek playwrights). However, common usage since then is exactly how Avaron is using it. In my opinion, both uses are "correct".
That said, I can see where Avaron is coming from: Here she's searching specifically for lesbian content and sees "female protagonist" in the tags. She thinks she's found a game that will follow Alenja exclusively (or at least the great majority of the time) and is disappointed when Yorik has his flashback scene where choices are
his choices, not a female character's. I don't fault her in the slightest for being disappointed or even a little upset.
I do think "misleading" is a bit strong, since technically "female protagonist" does still apply, albeit in a definition Avaron wasn't using. English is stupid in this way, because a simple text tag doesn't reveal
how a particular term is being used. While I personally probably would have assumed this meant the primary character of the game — allowing for occasional flashbacks, etc. — that doesn't mean everyone sees the word and takes away the same understanding.
Wet & Wild Production, perhaps a small update to the description (or a warning line below it) might prove helpful. Maybe something along the lines of this could work:
While this game does have a female protagonist, occasional perspective shifts in the story will involve other characters,
including both males and females. These scene shifts will usually including the need to make choices, even though the
player will not be controlling the primary character at the time.
That could clarify things, regardless of any individual's personal use of the term protagonist.
