Actualy if you saw him in person he is for sure Boston. Her has a tiny cork skrew tail like a boston and that picture doesn't show it but he is stocky and square like a Boston. The vet and I both think for sure boston.
I love besenjis and know a lot about them. I used to train and show conformation show dogs and know my breeds. Again if you saw his back end short legs and that is is a perfect boston backend and the way he runs is total boston.