There are a few good comments on the article page that point out that Military drones use an encrypted GPS channel that isn't susceptible to this specific attack. A much more sophisticated attack would have to be used to take over a military drone.
Military systems have never relied GPS for guidance. These systems were developed during the Cold War; the Soviets had the ability to take out the GPS satellites directly.
The US military has always used inertial navigation systems, usually based on extremely precise laser interferometers. You can't spoof or jam inertial guidance short of locally altering the laws of physics. A few decades ago, GPS was used to apply corrections within the (classified) error bounds of the inertial navigation system, which could be significant; any GPS correction outside the error bound of the inertial navigation system was interpreted as GPS being compromised. As the decades have passed, inertial navigation systems have become progressively more precise to the point that GPS is adding a rapidly shrinking amount of extra precision.
In fact, the US military is starting to test a new type of ultra-precise interferometer that allows inertial navigation to exceed the precision of GPS. GPS correct INS will only continue to be used to the extent it is inexpensive and gets the job done.
This scenario would also assumes that no human is in the loop and the drone is running on auto pilot. The "hack" was averted by the drone pilot switching the drone to manual in the exercise in question. I am not sure what military drones even have to do with this test.