Not sure what it is. But as a former patient in hospitals and many dr visits for different stuff i can say its not unheard of to have this done to you. Many of times i have had nurses pat my diaper after a changing. Usually on the butt area, but sometimes on the front right above the groin area. Specially at my urologist (them nurses seem to be the most prone to do it to you).
Why they do it is unknown to me, I think its because they like the sound or the feel of them. Could be a embarrassing type deal where they feel dominant over you and want to let it be known, who knows.
But i did notice that some of my nurses seemed to have really liked putting me into diapers. The latest one (who i swear was getting off on it) while in for a heart attack would check me more then any other nurse i had over my medical history. Always made the comment of "do you need a change" or "are you wet sweetie".
And when changing me always made a big deal out of it. did everything slowly and very well powdered and ointment rubbed in. This is the same nurse who would finish diapering me and after patt the front of my diaper above my groin area and say "there all nice n clean" while making the diaper crinkle by her patt's!!! Could have been a motherly instinct to her, or thing of looking at you like a child.
I find most nurses in hospitals especially, seem to think because i am in need of diapers i dont have the brain power to get embarrassed. I have had my diapers changed while a roommates family is present in the room, and i have been changed with my door and curtains wide frikin open for anyone passing thru the hall to see it. I have had diaper checks like a toddler while sitting in the hallway in a wheel chair (walk up grab your crotch and give a lite squeeze), while others visitors or dr's or whoever were passing where i was sitting.
So as far as nurses go i think its a caregiver mentality of "my charge and i will check & change how i want" deal to them. If its in diapers it needs to be treated as a child.
But there are some who you know darn well that just must enjoy putting people in diapers for one reason or another. Who knows maybe they cant have children of their own so they use you as it.