I believe that. I grew up in a town where stray dogs would form a pack and attack smaller dogs and sometimes people. It was a big problem for many years. Once, an out-of-towner told me he'd witnessed something strange happen in my town. He said he was driving through it when, suddenly, the police pulled up, stepped out of their vehicles, and started shooting dogs in the street. I said, "You mean that doesn't happen where you live?" Left on their own, dogs will form a pack and attack. I thought these packs were a common problem, but apparently not everywhere.
On some Indian Reservations in western Canada, once per year there’s a day when you keep your dog in the house or on a chain.
Otherwise, it’s shot like a coyote. That prevents feral packs from forming.