Most of that is due to college being an incredibly efficient social filter. The odds of a social interaction between Yale student and another being worthwhile (so to speak) are an order of magnitude higher than a Yale student and non-Yale New Haven dweller.
Back in my college (Yale), the campus and building layouts were pretty great. Some dorm complexes were much larger than city blocks, food was available in most living spaces. The ability to bump into people you know without need for mass planning is sorely missing from "adult" life.