Maps like this one are always problematic to interpret. There's three basic problems: the maps often do not represent depth of following, only its spread; the maps are not weighted for population; and a dot on the map represents a plurality, not necessarily a majority.
It does seem to show a wider interest than just the Boston area for the Eagles, but how solid is that following "outside of the beltway", so to speak? Is it representative of a true Massachusetts-wide following, or more reflective of another situation, like a generalized apathy for college football (such that one or two fans voting gives BC that region on the map), or since it's only based on I-A football, a variety of competing local interests? If, say, all colleges were on that map, BC probably would not have quite that large spread; local stats for UNH, Maine, and UMass might overwhelm BC (like, I'm sure, pockets of Connecticut and Rhode Island that are currently part of the solid green that UConn occupies might instead fall to URI or Yale).