If he was speaking specifically about Rome, then he is partially correct. Rome experienced terrible overcrowding as the Republic and Empire grew, over 1 million people at it's height. People did frequently live in apartment buildings that were prone to fire and collapse. There were slum areas of city, like all major cities. People who had lost money or land in the countryside came to Rome looking for work and when they found none, they settled in the poorer sections. There were gangs who patrolled the city and engaged in gang warfare just like now. Waste is a problem in any large pre-modern city (hell, even modern ones). Bathing was a part of Roman culture and respectability. There were public bath houses and public latrines, so if you're picturing feces and urine knee deep in the streets, that wouldn't be accurate, but it was there if people didn't dispose of their waste properly. Bath houses could be of varying levels of cleanliness as well. People also did a lot of their butchering on the streets so there was animal blood, animal parts, etc there. Household trash was also found on the streets, but Roman officials had people tasked with clearing major trash off of the streets. There was also graffiti as well- some of our best sources of every day Roman life and gossip comes from graffiti. Major cities often have the same features regardless of their time period or culture.

A History of the Roman People by Ward, Heidelberg, Yeo