I disagree. It should I think answer with a simple clarifying question:
Where is the car that you want to wash?
Are you legally permitted to drive that vehicle? Is the car actually a 1:10th scale model? Have aliens just invaded earth?
Sorry, but that’s not how conversation works. The person explained the situation and asked a question; it’s entirely reasonable for the respondent to answer based on the facts provided. If every exchange required interrogating every premise, all discussion would collapse into an absurd rabbit hole. It’s like typing “2 + 2 =” into a calculator and, instead of displaying “4”, being asked the clarifying question, “What is your definition of 2?”
And even then it would point to a heavy skew towards American culture with the implicit assumption that there must be multiple cars in the household
Why would you ask about walking if it wasn't a valid option?
You'd never ask a person this question with the hope of having a real and valid discussion.
Implicit in the question is the assumption that walking could be acceptable.