So they live in a world where Train to Busan is a movie and zombies are a part of lore

Actually, I thought you were referring to Train To Busan itself in this post, I didn't realise it was a different movie. My apologies.

Hell no, because in your scenario, that is one tiny piece of evidence! Now if I saw a group of them roll in doing superhuman shit, displaying fangs, drinking blood and showing an aversion to sunlight, then I'd quickly make the jump to vampires.

These things looked and moved identically to Train to Busan zombies, were killing fuck tons of people, and had a pretty good sized horde going, yet you had brain dead moves like principle refusing to call for help.

Hell, you had moron guy get bit after sticking a finger in a zombies mouth because he didn't want a clearly dead guy to swallow his tongue.

But it's also inconsistent. Didn't a woman zombie get a spear through the head, but kept on moving forward? (might have been upper torso).

I could have sworn they showed numerous zombies have either head damage, or get hit in the head, and not act fazed. But the archers hit them in the head for effect. It feels wildly inconsistent.

I don't know, people don't do their best in crisis.

And it's one thing to see zombies in a movie and another to assume that what you see in reality will act exactly like in the movies.

"I’m finding it annoying that it feels like the characters feel so helpless against them. I mean, they know “zombie lore”, so kill the brain?"

How would you go about that, exactly? The brain is a very well protected organ. The guys getting headshots with the bows is ridiculously unrealistic, as are headshots with pistols in other shows/movies. Trying to poke it through the eye with a broken broomstick when it's coming at you like that? Probably a bit easier, but still not at all easy.