Put differently - the human assumes that the other human will understand him or ask for clarification. Sometimes they are wrong in this assumption but no harm is done. With a computer: if the human takes the chance that the computer understands him OR will ask for clarification and the computer assumes a different meaning then there will be hell to pay.
Why? Why does the human get to slide but the computer doesn't?
Because the human is nondeterministic and the computer isn't. A computer, given a certain input, will always respond with a certain output. Humans, dogs, cats and most other animals don't do this. I'm finding it hard to understand why you have trouble with determinism vs non-determinism.
For the input "fruit flies like a banana", the computer must always EITHER ask for clarification OR assume what the sentence means. It cannot do ask for clarification some of the time and not others as a human will do.