They were using a small rotary wing (relatively cheap) research UAV, despite the various articles including pictures of Global Hawks/MQ-9s etc.
These small systems are usually designed for research, and so use the same UBlox/MTK/Sirf based GPS chipsets you find in sat-nav systems for example.
It looks similar to a Yamaha RMax, although I can't be bothered to find the actual model. The RMax is designed for agricultural use & research, not fighting wars.
The vehicle control software simply assumes the GPS is correct. It wouldn't be that difficult to cross-check against the IMU data - our research drones can happily fly for a few seconds if they loose their GPS lock but spoofing would probably knock them down, because we just assume it won't happen!
You could build a DIY version of the Texas drone for around $1000 using open source hardware and a COTS model helicopter.
This not news, anyone who works with these vehicles knows this. It's like shooting a horse and then claiming terrorists can take out tanks with a single bullet.
You could as well use a replay attack against the pilot's control system (probably on 2.4GHz) using much cheaper hardware.
There is still plenty of work to do before these class of research drones become commonplace overhead - in particular, practically every onboard system is a single point of failure.
If you are comfortable would you mind linking to your homepage or sending me your contact info? (You can find my email at dylanfield.com) I'd love to talk more with you sometime.
Edit: yep. It's from Adaptive Flight, Inc. which is a modified Logo 500.