Typically, saying they 'rented it out' implies that the organization had exclusive use of the facility for a period of time. That was not the case here.
You are making a rather broad assumption, but nevertheless, I presume they “rented it out” to the day camp organization for use one day a week for a set period of time (which is unknown to me).
Call it what you will, they did what they did, and I would guess, with knowledge up front with whom they were dealing.