Jerome of Sandy Cove - A castaway with both legs recently amputated, and who never spoke for the rest of his life

I see this as the most likely explanation

It is possible that Jerome's difficulties with producing speech could be linked to a brain injury, most likely in Broca's area, the part of the brain that regulates speech. Jerome would have been incapable of speaking in any sort of understandable language.[1] This may account for Jerome's ability to make animalistic noises, but not replicate human language.