Per People magazine, it wasn't Ryan that called 911. Ryan was the one providing the CPR. This makes more sense. LINK
By this point Allemand was lying on the floor, and the 911 operator told Simpson that they needed to do CPR. Anderson, who was crying as he leaned over the unconscious 29-year-old, started doing chest compressions.
Realizing that they needed more help, he screamed down the hallway, "We need a doctor!," and a nurse from a nearby apartment took over the compressions while Anderson began doing mouth to mouth.