Probably because they’re not really the same person? I like to think that the Green paired with Pixiv!Red is a separate counterpart as well, as none of the others has green eyes and an Eevee or Squirtle (I’ve seen him with a Bulbasaur and its evolutions as well - no known other counterparts of Green choose it as a starter). He also has an unique personality, so why not make him a counterpart? :/
That works as well. In fact, I did think about that more than once :P
Red: Uhm… I remember catching a Krabby for the Dex, but it’s been in the PC ever since. Are you somehow mistaken?
Green: …Am I supposed to laugh?
"You’re so gay that it disgusts me."
"…So are you."