ER lived in 'the nerd house', because he was a nerd - he was the most shy and retiring of all of them. In places like Isla Vista there is a clear
hierarchy of student homes by the popularity of their inhabitants, where students of equal social rank group together in joint private housing. Via informal networks and fraternities and sororities groups of guys and girls are formed who will arrange to live together.
A process of social sorting happens in the first year. And it determines what your college experience is gonna be. Make-or-break.
Elliot always was on the margins of Isla Vista student culture - he lived in a house by a commercial service that just assigns you a house and housemates for a charge. If you live in such a house you are on the margin, on the fringe. Low status, nerd-tier, obscure immigrant-tier, incel-tier housing where you end up and stay 'stuck' if you don't know anyone and have no connections.