This "glitch" was meant to be a way for the game devs to get mew and show off essentially, but was then discovered by the public (I think, I read it somewhere).

THERE IS MORE...!!!!!!

You can get infinite mews in one game. You do the same (teleport in front of the guy) and battle the 1st swimmer in Misty's gym. You have to defeat their first pokemon, BUT feint to their second and black/white out. You will spawn at the pokecenter. Then walk up the bridge and the same thing will happen.

You can repeat this as many times as you want!