It was a young pilot whale or 'false killer whale'. They regularly slide up onto the siding and back into the water but this one hasn't mastered it yet. The trainers were told not to interfere (per SeaWorld) to allow the animal to learn the behavior on its own. After about 30 minutes, they did end up pushing it into the water. According to John Hargrove, former SeaWorld trainer and current anti-captivity activist, the animal was in no danger but clearly stressed from being stuck. I'm surprised this has received so much attention as I don't consider this anywhere near as wrong as other SeaWorld actions, specifically their captive breeding/artificial insemination and general slave circus with their killer whales.