Pumas don't dislike water as much as some other cats. They're not quite as good swimmers as Jaguars, but some of them live on islands and swim for over a kilometer to go to new territory.
Maybe it was young and hungry. If the big hairless bear gives you food and water, you might think it's only fair to let it touch you.
And typing this, this sounds awfully child-abuse-y. I want to emphasize, that I'm referring to large cats and petting in a manor appropriate for felines.