Wait... In the USA it's not mandatory to screen the electronics separately?
All around the world I've been to, you have to place the laptops, tablets and somesuch independently through the scanning machines. It is quite a pain to do, but it is precisely to make these sorts of findings faster and easier.
Well, good thing they found it anyway.
Regards.
In the US at least there is a thing called "TSA Precheck" where you essentially are "pre-cleared" or trusted to pass through security without removing your shoes, belt, etc. and without removing your laptop from its case/bag. I use it when I infrequently fly and it's a much faster and invasive way to pass through security. I don't remove any clothing, not even my jacket, and just put my phone, wallet, etc. in a little basket separate from the laptop which is in the case with other things like pens, paper, charging cable, etc. However, I could see someone trying to take advantage of that fact and trying to pass dangerous goods through.