Check with your local DMV. Most states require you to register your vehicle in 30 days or so after moving there. If someone is using the roads in your area but isn't paying their fair share, that's money out of your pocket (and all your neighbor's pockets). Some people try this to avoid smog testing, and that gets to be a health issue, especially in non-attainment areas.
MA has a reputation for high insurance rates, so I doubt if avoiding a higher premium is an issue here.
And it could be that the person just seems to live in NY but lives long enough in MA during the year that MA is their legal residence.