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.
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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.