It’s probably gone down, actually, at least in per capita terms. Boston’s population is a lot bigger than it used to be, so that has to be taken into account.
The comparison is between today and ‘today but without the highway’, not between today and before the highway was built. If the population increase is greater with the highway there, that’s still part of the induced demand.
Boston is far from car dependent; it’s probably one of the worst cities in America for drivers, and best for cyclists and pedestrians.
A city being “bad for drivers” is not a great indicator of it not being car dependant. Cities in the Netherlands are probably the most walkable and bikable on the planet, and also great to drive in because there are hardly any cars.