that's an IOS software update which kicks in as
download as soon as there's a power source (I think) and a Wifi connection.
I don't think you can disable this automatic download in IOS.
however, if you don't want to update to the latest, coolest, slowest, most annoying
IOS,
you could dis-allow the Apple software update website in your router so that iPad can't call home even if it wants to.