I can't be 100% certain, you know, since I don't speak lion, but I do believe that lion told that alligator if he come out that water he gone have some problems he don't want. Lions roars are heard up to a mile away. So imagine what that croc was experiencing. He was intimidated as most animals would be. The roar....and those damn muscles. Lion is definitely in his prime and will lose very little if any fights at this stage in his life.
And apparently the mr. alligator understood & didn't want any problems.
1 Article Title "Who is The KING?"
Laos Adventure Travel - And What an Adventure!