I've inadvertently ended up in the water with stellar sea lions before. They were as surprised to see me as I was to see them. They are BIG, but I'm not sure in retrospect how aggressive they are towards people. One big male was flashing his teeth and took an aggressive stance towards me, but I still don't think he was trying to eat me. Bite the shit out of me, maybe, but I don't feel they saw me or the poor little girl as an actual viable meal, despite their 2500lbs of awesomeness.
When you feed a large marine opportunistic carinovore as casually as you'd feed a duck, you're asking for trouble if you get too close.
I was spear fishing around California sea lions years ago and when they bit at my fish, they bit and RAN, and don't let go. It looks to me like the seal in the video thought he had an easy meal (the white of the dress, which could be mistaken for a lot of different fish in that area), realized it was attached to something it couldn't eat, and let it be.
Last summer I ended up in La Paz. The California sea lions there were soooo friendly, but it was always a bit weird when they'd kind of gum your skull. Always seemed like a warning ("I could literally crush your skull, small human.")
The animals in that video had at-least 1,000lbs on most California seals I've seen, they could do serious damage, but it's pretty rare to hear it happening.
Leapard seals, different story.