The tree in the middle of the clearing sometimes changes when you enter the area.
The game basically flips a coin to decide whether you get the big tree or the small tree.
There's also an unused third variation, with the tree missing.
I think this is a very half-hearted attempt at a "randomly generated" jungle, to make it feel like Guybrush is encountering the monkey in different places, but it seems like the developers didn't really commit to the idea.
The grey monkey we meet on Monkey Island is never given any name in-game, but he seems to be called "Jojo" in the source files. Specifically, the costume for the tiny monkey shown on the map is called "little-jojo" (while the monkey's regular costume is just called "monkey-skin").
This probably explains why the same monkey is called "Jojo Sr" in Escape from Monkey Island. The MI4 team must have correctly remembered the MI1 monkey being named Jojo, but maybe weren't aware that the name was never mentioned in-game.
Confusingly, "Jojo" also happens to be the name of a different monkey in Monkey Island 2. More on that here.