I worked in property management for several years, and aside from dog issues, the main complaint of homeowners was someone taking "their" parking spot. Legally, they don't own the spot unless it is on private property and has been assigned to them. However, neighbors show courtesy by allowing everyone to park next to their own house. (A big deal when you're coming home in the rain with an armful of groceries).
Homeowners are expected to inform visitors of parking policies, so your boyfriend should have mentioned something to you. However, as I said, it's not illegal.