What's humane?

This is a heartwarming story: Meet Forrest Hump

Here is how it starts:

The camel’s dark oval eyes were glazed, the lids only half open. He lay on the ground in his pen, his mangy flanks quivering with each labored breath. That November morning, Roger, our animal director at Boys Ranch Town, a 145-acre farm for troubled boys on the outskirts of Edmond, Oklahoma, had come to me, worried. “I can’t get him to stand,” he said. “He’s rubbing holes in his skin by dragging himself around.” Now I watched anxiously as the vet I’d called looked the camel over. Despite arthritis and wobbly joints, the exotic creature had become an integral part of our program since he was donated to us a couple of years ago, teaching the boys the responsibility of caring for an animal, and even starring in the scene with the wise men in our annual drive-through Christmas pageant. He was as friendly as a great big puppy, and the boys loved Forrest Hump, as they called him. Finally, the vet finished his examination. “Your camel has progressive, degenerative joint disease,” he said. “He’s not going to get better. The humane thing would be to put him down.”

I've never quite understood why "putting down" an animal with generative joint disease is "humane" [human], but forcing a human with painful generative joint disease to go on living is humane, and assisting them towards death is murder. I don't know who is right, I only know that it doesn't make sense. You'll have to read the story to see how they decided.