On the one hand, it is pretty touching and cute. Despite the Aerosmith song. I mean, the best thing to come out of Aerosmith is Liv Tyler and, let's face it, that's not a lot. So, yeah, I'm not immune to the cute factor.
On the other hand... guys, that's a friggin lion. Two guys adopted a large, predatory cat as a pet and then gave it up. They then flew to Africa to see it after having been warned that it would not remember them and would probably be dangerous. So, in short, these guys could basically be on the cover of "Poor Decision Making Monthly". They could probably also have a spread in the "Quarterly Journal of Questionable Religious Puns" for naming their Lion "Christian." Not that there's any unpleasant history summed up there or anything.
I'm reminded of nothing so much as those guys from my home state who adopt alligator young and decide to raise them as pets. At least lions are social critters and make a distinction between "my folks" and "not my folks." Gators, on the other hand, are quite solitary and really divide the world up into the categories of "food," "thinks of me as food," and "boring." And guys, honestly, gators don't put many things in that second category.
Here's an idea: next time, go with a house cat.