I update in favor of "user 75th is more experienced in the tropes of enigma fiction." Indeed I would not be at all surprised were I to discover that user 75th writes such fiction him or herself. It similarly wouldn't surprise me if user 75th had gone to the library and checked out and read some of the same 15 books Elizier checked out and read before writing HPMoR.

For example, before reading the author's notes on HPMoR I was not familiar with Chekhov's Gun. Now that I am, I am much more likely to catch such a device when it appears in other fiction. I now suspect user 75th is quite familiar with Chekhov's Gun and other standard tricks of this sort of story. 75th picked up on one such trope (one I'm still not familiar with) that signaled that Hermione was heading for death.

If there's a general update to be had here, it may go something like this:

Before dismissing those who speak with what I think is too much confidence, I need to consider the possibility that their confidence is based on facts or experience I am not aware of. I should probably take five minutes to ask them why they are so confident before dismissing them.