PIP

I recently attended a PIP interview with my son who is cared for at home and received middle level care DLA and lower level mobility DLA, which had been awarded for life. Much to my surprise he was asked what he spent his money on. We were not expecting that as I had not spotted anything in the advise (but I am quite capable of missing it!)
1. Was the interviewer entitled to ask that question?
2. Is the answer likely to impact his eligibility?
many thanks