Police Checking

Situation:
Police checking for drink and driving
Myself and my friend driving back home after dropping a drunk stranger home
Action in question:
Police stop our bike and start checking
The driver(myself of course) removes the helmet and gets checked for drinking and driving
The constable after clearing me goes to the pillion rider(my knowledgable friend)
He removes his helmet and gets checked for drinking and sitting behind on a bike (@':-).?:@!)
Almost 2 kms after this my friend wonders what is the neccessity for a pillion rider to get checked for drinking and driving