Like the article says, maybe he would prefer to die earlier in his own habitat than in a large swimming pool.
I say we ask Tilly what he wants. If he doesn't respond we can only assume all is well. Who are we to guess if it's better for him or not? Or better yet why do you even care? Do you also cry for mice that get killed in your house from a mouse trap or rat poison? Do you cry for ants that get stepped on? Why should we protect killer whales and not other forms of life?