I think they’re making connections where there aren’t any. Almost all of these little stores are owned by ME immigrants (Jewish, Muslim or Christian) or Pakistanis, and I doubt that the killer knows their religions. The shops are open late and these shopkeepers usually work alone and don’t have surveillance cameras, so they’re probably victims of opportunity. It does sound like there’s something weird to the number part of it, though.
If your theory is right the police may want to check the videos of businesses that do have cameras since the killer would case the place first.