not to be a fusspot but...
It isn't anywhere near what we'd call mature. You can buy them that big. A few years ago, "Terrain at Styers" was selling them that big if not a little bigger - for $1300. There was a bigger one in Columbia, MD, that died after a hot summer.
At any rate, the issue with them from NYC south is more "summer hardiness", not winter hardiness. This is obviously colder than NYC so, yes, its winter hardiness would be impressive...if we find out it had survived both last winter and this winter w/o protection. (FWIW, Ian out in WA state is aware of some that have survived -10F or slightly lower) You should approach the owners if you're back in the area at a better time of year. (I'd be annoyed having to open my door for a stranger with this weather...although their door appears to be open!) Could they have used wiltpruf, for example? A lot of the issues our winters cause is due to drying out with a plant like this, not the cold per se.
Anyhow, still a good find...we should keep our eye on it for the next few years. Hopefully the house won't change hands and someone will think "I don't want this monstrosity in my way every time I leave my house".