vintage Gazelle I spotted nearby a year ago, had a Dutch shop sticker on it. The bicycles' owners must have at some point brought them on the plane when moving to Boston, probably for grad school or for post-doctoral positions.
I think that to spot several bicycles like this in an American city is highly improbable. Surely it is proof that Boston is the vintage bike capital? If you have a better story about your city, bring it on!