As far as I can tell, he was riding on the road. She was on her phone and stepped in front of him.
I'm not saying this is what happened, but you know how it is: They see you, then step one way, and then panic, change their minds and try and step back the other way. You already changed direction once to miss them, but when they step back, you can't get off a collision course. You didn't brake at first because they stepped one way and you steered the other. I've had that loads of times, but I'm always ready for it and able to do an emergency stop. The worse case is when there's to people and they step different ways. maybe it's the herding instinct, but one will always try and reach the other at the last moment.
What I find most annoying is that they shouldn't be there in the first place. If they only stuck to the segregated footpath, nobody would have to suffer any stress.