It is interesting to see how many comments seem to forget that the setting for this is basically 2020. I had to go around a large city more than once during the major lockdown period due to a burn and it was pretty much like a zombie movie.
The rare person you saw going around, most likely taking a dog for a walk, would pretend not to see anything and keep their distance. Police patrols were virtually non-existent. So it is perfectly reasonable for the MC to have stayed in the park for 3 days without being bothered.