Lanefan
Victoria Rules
It's that the specific information has been shared, where that specific information wouldn't yet be known in the fiction.Yes, this is about GM constraint. These things are put out for the table to see and therefore the GM has committed to them. The players are aware and cannot be deceived on those items.
And your list of 1E equivalents and how that’s “disclosing too much meta” misses the point entirely. It’s about the specific information that has been shared.
When you've never seen any of the father, daughter, or Kraken before and thus have no idea what makes any of them tick beyond the obvious (e.g. she's small, the beast has tentacles and can swim), why do you expect to be told exactly what their mechanics are?The mechanics of the game are the translation of character info to player info. If you don't expect adventuring PCs to have some sense of what the father is capable of, or what benefits the daughter may be able to use, or what manner of threat the monster may be, then I’d classify that as totally immersion breaking.
The father, for example, could be a common-joe fisher or a 3rd-level Fighter in the army or a 12th-level Wizard who's retired to raise his kid; but until he does something other than row a boat you have no way of telling.
The daughter could be a polymorphed demon that the father has just summoned the Kraken to devour; you can't tell.
And in older editions where illusion spells were actually useful, the whole damn scene could be somebody's afternoon entertainment.

I don't see these things as an either-or. I generally prefer the mechanics stay out of sight until they're forced to rear their ugly heads, but I also tend to dislike being railroaded and can usually tell if-when it's happening.And for me, and I expect many others, being railroaded is the most immersion breaking thing that can happen. This is why I prefer player facing mechanics and practices.
It's the same way I view cars. I love driving the things but I've no real clue - and don't much care - what goes on under the hood as long as it runs reliably and gets me where I want to go.