Beyond any of this though:
Why would blizzard write the story to have Thlassian Elves in the horde calling themselves High Elves to begin with? For the sake of understanding the story that would just be confusing for a lot of people. Why would you want to call the elves on BOTH factions High Elves rather than those groups having their own names? It’s simple and easier to understand. There’s no need to muddy the water when each group of Thalassian Elves have their own name.