Just because it doesn't matter to you, there's no reason to be dismissive of what matters to other people. I try to think what the world would be like if magic was real and things really did go bump in the night.but all the time they would be exactly like the DM played them to be.
If this causes disruption in a campaign based on NPC reactions it is because the DM wants it to cause such and plays those NPCs like that.
This is essentially a "DM agency" issue. The DM can choose to make all of his NPCs nonpulsed about it just like a player can use his agency to make his PC who never saw a dragonborn non-pulsed. If the DM chooses to have his NPCs get excited about it, that is because he excersized his agency over those NPCs and chose to do that.
No. The DM can make the tavern keeper do whatever he wants in game and he doesn't have to explain it.
This is no different than a brand new PC showing up inside the pocket plane where the last player died with no explanation. Whether it is how it would be IRL, it is entirely possible for the DM to do/allow in game and won't break the game at all.
I think the whole "that is not how it would be IRL" is a bit overblown in a game with Fireballs and Dragons (or walking skeletons if you don't have dragons).
You don't care? Fine. I do, and I feel like my campaigns are better for it.