Legal question for as a landlord in Nevada SFR

I have a large 5 bedroom, 3.5 bath house for rent in Nevada.  I had someone call that is interested in it.  I asked how many people it's for and what the income is. It's for 1 person with the proper amount of income from disability.  The disability amount is more than most professionals make.   I asked why this prospective tenant wants such a large house for 1 person, and the answer was something like  I don't really have to tell you that.  If I have the income and want a house that size, I don't need to say why.  Is it legal for me to ask why 1 person wants such a large house?  As the owner, I'm wondering how the house will be used.  I want to follow the law, but want to know if legally I need to consider this type of renter.