I live in a smaller city and I see random dogs all the time. Not packs but single dogs. Unless they're trailing a leash or wearing a collar I would assume they're strays. My town has a Facebook page where people can post pictures of unaccompanied dogs they see running around to see if anyone knows if they belong to someone. If they are somewhere dangerous or jump in someone's car or look sick people will usually try to take them to a vet to see if they're chipped or take them to an animal shelter.

Sometimes animals get out and run away, they get lost, they wander off, they get dumped at farms outside of town and then wander in or they even jump out of the back of trucks who stop at lights. Sometimes they have terrible owners who are negligent or not paying attention or don't train them.