That doesn't make it less disappointing; also I think it's actually more likely that it used to be a real clue, but the author changed his mind about how the story went -- that's also disappointing.

There's the third possibility, that it used to be a real clue, and it is still relevant in how the story is going to go; but that Harry himself, the character, shouldn't have heard about it so early, or he'd wonder inappropriately over it.

Alright, granted, those are possibilities. I'm not certain that you're correct, but they are valid.

I'm having trouble imagining that in a HPMoRVerse with an actual competent Dumbledore, Hagrid went alone to retrieve baby Harry.

Hm. Okay, I understand that, but I would not expect anyone, really, to spend a great deal of time searching through the rubble when Harry still needs to be taken care of. Yes, they could Summon it (assuming it was Summon-able) but only if they were looking for it specifically, if they thought it wasn't destroyed in the explosion, etc.