shutting door to toilet

My cantonese wife's cousin was staying with us from Hong Kong the past
weekend.  He is a well-educated fellow, who attended the best private
schools and universities since his family is one of the wealthiest in
HK.  To my horror, he did not shut the bathroom door when going to the
toilet (number 2).  When  Ira asked him repeatedly to shut the door,
please, he laughed and insisted that this is not the chinese custom
when only family members are in the house.  Is this true?  Ira really
doesn't want to watch him sit on the toilet and read chinese girlie
magazines.