Tufts is an excellent school. Even if he wants to be pre-med, who knows how he'll feel in two or three years? You shouldn't choose a school based SOLEY on your intended career goal when the difference between it and another school is not that great. Is Johns Hopkins one of the absolute best places for pre-meds? Yes. Is Tufts a good place for pre-meds? Of course it is. It's a good place for anything.
Your friend may even have an easier time getting into med school from tufts since it may be easier to get a higher GPA there, due to less competition from other pre-med undergrads.
Also, I doubt that he chose Tufts based on proximity alone. That may have been the single most important factor, but I'm guessing he visited all the different campuses, and he liked Tufts' more, maybe due to its proximity and some other intangibles.
In any case, he didn't make a "wrong move." Turning down Hopkins is not like suicide for premeds.