I had a neighbor who was feeding my chickens and later called the animal control on us for them pooping on her ramp. (She also has a lot of cats and feeds all the strays around.) In my neighborhood, the landlord is a farmer and allows people to own whatever livestock that we want (though he doesn't recommend horses or cows due to the small lots). Despite this, the animal control officer still came and threatened us if they get called again,  they will take all of our chickens and we would have to pay to get them back (plus pick them up from wherever they would keep them.) To deal with this,  we ended up downsizing most of our birds and built runs to keep them in.
With a stray chicken running around,  I suggest you keep your flock far away from it, and everywhere it's been. It could be carrying both diseases and parasites that you don't want your flock exposed to.  Also, with so many cats around,  without some guard animal to keep them away, I don't suggest you free range your flock anyways. Cats are on the list of chicken predators,  and I have had a few that attempted to attack my birds. (Cat attacks are bad, and with the added bacteria from their nails, they're often fatal.)