To be cheek by jowl is to be positioned very close together, and in this sentence the people are living in close proximity to each other.
Context: "The city of Philadelphia lay just out of sight; he could smell the haze of fire, the stink of thousands of people living in very close proximity to each other."
Hypothesis: The city of Philadelphia lay just out of sight; he could smell the haze of fire, the stink of thousands of people living cheek by jowl.
Based on the context, is the hypothesis true, false, or unknown?