A lot of restaurants close around 9pm or 10pm.
I think he's referring to the cultural difference where Americans typically eat dinner between 6-9pm and Mexicans eat later starting 9pm. So the takeaway is if you want to eat an early dinner then maybe seek out a restaurant that caters to tourists and if you want to eat a late dinner then look for a restaurant that caters to locals. In this case, many of our recommendations (Los Tacotales, Los Seras, etc) cater mainly to locals although they have developed a significant follwing among seasoned travelers.
I don't know that a lot close that early, maybe midnight but you get back on 30 and stuff is open till midnight or 2am - the other night a full house at 3:30am at one place lol