I think you are right, Mike. These fowlers were definitely made and used in New England in the late 17th and early 18th century era---and even later. I've seen several in the Marshfield/Duxbury area over the years.
When I was a kid we lived in old houses and many doors had handles that resemble this style of trigger guard. Or the trigger guard resembles the door handles--in any case, I think they are pretty cool. And this is a very cool fowler!