Most of us have asked someone a question or said something to someone only to have their response to us make it clear that they did not understand what we said.
Is that why your relative gave “off-the-wall” answers to the census taker, records clerk, etc.?
A person’s difficulty in understanding the question can be compounded by age, hearing difficulties, cognitive abilities, native language, etc. Do not assume that your relative really understood what they were being asked.