1) Agree - stereotypes are bad; a good example is "all asians are good at math".
ANY stereotype puts pressure on a person to be a certain way and that's not cool, would be the simplest explanation.
2) Zep wasn't necessarily stereotyping, you could easily be misunderstanding intent.
Zep could simply be stating in fewer words "I've been to the asian market, and they literally all wear masks there, so I will go there". Not saying necessarily "all asians wear masks" but rather just "this neighborhood wears masks". I don't believe it's necessarily stereotyping, given his wording and context.