She probably just felt he was creepy at first and then it all happened so fast. It's also always super easy to
second guess what someone could've or would do. But reality is often far different. I think they were recording themselves when they noticed the guy and kept going to capture the "creepy guy" menacing them. But when he suddenly came up super fast she probably dropped the phone into her pocket fast without doing anything else, so she could have her hands free to maybe defend herself.
She may not have knew it was a real danger until it was too late to call 911.
Also, with adrenaline rushing people don't always think perfectly logically. Some people freeze a little and/or go off instinct.
I had a situation where a person jumped up off the ground in the dark where I was parking my car and began screaming (unearthly) and rushing toward me. It was sudden and totally unexpected. I managed to quickly reverse my car into the street but once there my hands were shaking so bad it took me well over a minute to be able to dial 911 as this crazy person stood in the parking lot staring at me.