A) Baby animals have natural instincts that cause them to fear things that are bigger and more threatening. Of course it doesn't know it's a lion. Black bears in their natural habitat are just about as far as you can get from the Serengeti. However, before this scene was shot, the bear was held up to a window in front of two lion cubs, which both swiped at the bear and showed their teeth. He saw enough to know to be afraid. And bears are only apex predators within their own regions. Pit one against a lion or a tiger and I bet the cat would win out.

[ETA: Turns out black bears aren't even apex predators in their natural range: "Despite the black bear being more powerful on a one to one basis, packs of wolves have been recorded to kill black bears on numerous occasions without eating them. Unlike brown bears, black bears frequently lose against wolves in disputes over kills.[59] Wolf packs are known to kill black bears during their hibernation cycle.[33]" (Via Wikipedia.)]

B) That lion is showing classic cat posturing that demonstrates a fear response: crouching low, ears back, tail tucked. Actually, it seems far more terrified of the handler than the bear, which makes me wonder what else has been done to it.

C) Everland Park, where this was filmed, is Korea's largest theme park. They are not a nonprofit organization. Therefore, the care and keeping of these animals is solely for the purpose of monetary gain, and anything they do with these animals can be considered exploitative. They breed white tigers and ligers, which are both abominable practices, and they house their tigers with lions. The cats have been caught on film, fighting and injuring one another, and then park did not intervene to separate them. They clearly do not give two shits about these animals.

By the way, if you're going to "socialize" any wild animal in any kind of meaningful way, you do it with members of its own species, not with something that has demonstrated a desire to act aggressively toward the animal.