Seconded. They are not laughing at your misuse of the word grammatically. They are laughing at the unintentional parallel to the way bigots talk about the people they target with their hate/insults. For a joke, they are twisting the meaning of your words to imply that when you say “those people” you are referring to some minority or marginalized group in a derogatory way. “Those people are loud” is an innocent statement on it’s own when referring to a group of people being disdisruptive. But “Those people are loud” when “those people” refers to an entire demographic of people is a derogatory stereotype. “What do you mean thoooose people?”