How are the Squid Game guards chosen?

How are the Squid Game guards chosen? The idea is that when the recruiter played by Gong Yoo offers someone a choice between red and blue tiles, that if they pick blue and play, they end up as a Squid Game player. But if they would have picked red, they would have become a guard, one of the faceless, PlayStation-mask wearing enforcers we see in the show.

The idea is that when the recruiter played by Gong Yoo offers someone a choice between red and blue tiles, that if they pick blue and play, they end up as a Squid Game player. But if they would have picked red, they would have become a guard, one of the faceless, PlayStation-mask wearing enforcers we see in the show.