The man in this video describes it perfectly.
“Never in my life have I seen kittens drowning in the river. Or swimming.”
The man and his buddy holding the camera waited for other cats to arrive after two of them came swimming towards their boat. It was obvious that they were drowning.
While the man and his friend cannot ascertain if someone threw the kittens into the river or something more vicious, the two kittens are safe. Hopefully, they are only the two in the river as it would be painful to think if there are others who had drowned.