DOS2 and the DOS4 Engine BG3 runs off of, uses a TAG system... the race stuff is specifically set up for the TAG system.
Selecting the race selects the tags.
It's not intended to be an advertisement that tells us they aren't Elves. They just need to make it easier to access the TAGS so they can streamline niche replies or quirks attached to each subtype.
This! Pure engine thing, to simplify the already herculean work they had to do by adding DnD rules to the DOS mechanic.
I am personally more curious why my Half-Drow (that is listed as a sub-race for Half-Elves) is recognized everywhere as a pure drow without an option to correct anyone once "HALF-drow!". Shadowheart does get to say "HALF-elf".
