[julian37]

This is addressed in the article, and arguably the article's main point. Quoth:

"I have to say that something I thought would be a big issue is the vagueness of natural language. That one particular natural language input might equally well refer to many different precise programs.

"And I had imagined it would be a routine thing to have to generate test examples for the user in order to be able to choose between different possible programs.

"But in reality this seems to be quite rare: there is usually an “obvious” interpretation, that in typical Wolfram|Alpha style, one can put first—with the less obvious interpretations a click away."