The Bell 47G helicopter Tongo flew to the island in is quite loud. The castaways would have heard him approach and land.
The so-called Gorilla looks like an Orangutan.
Tongo can't be "half ape and half man" since all men are apes.
In some scenes the Ape Man is wearing shoes. In others he is barefoot.
Towards the end of the episode, the castaways read Tongo's note that he can't take them back with him because of how he behaved with the gorilla. Mr. Howell yells "We won't tell anyone!" followed by other random comments from the others for Tongo to come back. Tongo leaves and as the camera pulls away from the castaways, the same audio repeats although this time it doesn't match what anyone is saying.
In the last scene it is clear that the helicopter pilot, not Tongo, is actually flying.
Since Tongo obviously didn't know there was anyone on the island, why exactly did he fly there in the first place?
When the castaways are shouting at Tongo, who is flying a helicopter, Mr. Howell is twice heard to shout "We won't tell anyone!" But the second time, his lips don't move.