So I don't fly with a tablet any more haha! Although, I get that time has passed and I would no longer be accosted so much, I assume. Must be pretty common now. My story takes place in ~2011 with the Motorola Xoom tablet. I guess they had never seen a tablet before.
I was also working hard on a plane one time, writing code to access barometer data on mobile devices to build a distributed weather sensor network that could be activated in software. The flight attendant came by and told me, "okay, time to put your toys away sweetie" referring to my tablet and phone. Oooooooooh my god.
That said, security rules vary from airport to airport. SFO with TSA Pre is practically a no-op, but CDG security requires that you remove from carry-on any device with a >20cm dimension!
Pre-iPad, most airport staff (who aren't hardcore techies, or might not have the privilege of higher education) might think of a tablet as a laptop anyway.