[[WMG: The whole film is Professor Bomba telling somebody the story.]]
This would account for the somewhat disjointed storytelling, seeing as Bomba himself is more than a bit scatterbrained.
[[WMG: Professor Bomba is slightly faster than ordinary humans.]]
When we see him from a non-Leafman perspective, he often seems to be moving and reacting and talking too fast. Also, this would explain how he discovered the Leafmen. If his speed differential is less than normal, he'd be a bit more able to see them naturally.