To clarify and give a little more information:
Crim was at a crossroads: they could either choose to be human or choose to be a vampire. The special capsule will transform them fully into either, because being mixed can cause some real issues... like the one where they nearly killed their childhood friend when they were young, and as a result their memory was wiped.
Crim wasn't told this, because their parents wanted Crim to choose without any pressure, and what's less pressure than choosing a race for a game character that can normally be changed at will?
The pod will take, iirc, 3 months to transform Crim, and so for now the story is all in-game, but the WN does get back to their reality once the pod is done its job (according to other comments in previous chapters).
I don't think the author forgot their initial premise.
What I don't know about, and what would be interesting, is if the unique race thing is expanded upon to the rest of the players.
- Crim has vampire as their in-game unique race.
- Unique races aren't available to every player.
- Crim has real vampire DNA.
Hypothesis: Unique races are the game detecting trace amounts of monster/mythical DNA in players, and theoretically, if they were to use the pod Crim is using, they could also transform into that race. Thus, Crim's parents' end game could possibly be to kick-start the return of a world with once extinct races.