Too many unknowns to be sure. It looked like a swamp rabbit, which are adapted to and comfortable with swimming, but I’m not an expert on wild rabbits.
It might well have jumped in to avoid a predator we can’t see in the video. They have excellent hearing, sight, and smell, and so may have detected a threat somewhere off camera. They are naturally skittish, and often treat anything unusual as a threat. Or maybe it wanted to find food. Who knows?
Rabbits can be weird. Mine will often stare at a wall or out the deck door and thump the floor repeatedly in warning. When I check I don’t see anything, but maybe he detected something: a fox, owl, the neighbor’s dogs inside his house, a car in the distance. He’s even tried to get me under the couch during a thunderstorm. Little guy was worried about my safety. 
The rabbit in the video seemed comfortable with getting wet, but that isn’t true for domestic rabbits which were originally bred for meat and high quality fur before becoming more typical pets. Water can be very dangerous for them. They are fastidious groomers and generally don’t need help keeping clean.
I’m vegetarian. 
