Odd that you mention that they were likely homeless.
I have noticed a quite a few good tricks the homeless people use.
For a lot of them cities are very hostile environments, even worse than a desert.
In the city I live in now there are a number of homeless people who sleep out at temperatures in the -20 and below range.

Some of them are true experts about stealth camping in the concrete jungle.
Not only do they have the regular bush craft problems coupled with a lack of equipment, they need to avoid attracting the attention of police who will hassle them or the violent punks who might kill them just for fun.
Count with that the fact that as soon as the city or the businesses people figure out where homeless people are sleeping they take steps to remove that option.

It goes far beyond just sleeping on a park bench or under a bridge, and some of their solutions are quite brilliant