There are prosumer gas powered ones coming out. My guess is it could be a version of this NASA project that can hover and then transition to winged flight. It's unclear how good of a look they got at it.
Blog comments are mentioning the fact that one of the choppers had to refuel, maybe a testament to how energetic the chase was, but maybe it was already low at that point. That, and the fact that there is an AFB there points to a military drone.
If it's performing maneuvers as complex as described, it must be heavily computer assisted or computer controlled, so you'd presumably need sensors, computer, etc, that adds a lot of weight. On top of that, the speeds they describe coupled with the wind they said it was fighting, it would need to be very well built. Given all the factors, I think it would probably have to be extremly extremly advance.
Sensors and computers aren't meaningfully different for a 5' quadrotor vs a 5" micro. Same physics, same control loop.
Yeah but you can put a radar and nice camera on the 5' one.
Sensors and computers weigh next to nothing. Every piece of cheap plastic commonly used for building quadcopters fulfills your criterion of being 'very well built'. Nothing about your description makes a drone 'extremely advanced'. Just a hobby project of some random guy/gal.
Computers are 100% required for motor coordination and other low level flight details with a multirotor uav, but in terms of piloting the aircraft a typical human brain is quite capable with practice.
It's nearly trivially easy to build one, though not necessarily cheap. Just replace the battery pack with an engine, generator and fuel. It may be necessary to use a turbine engine to meet requirements, hence not cheap, but for flight control you just need to use free open source software firmware (Ardupilot?) that has long been freely available and tweak it.
I think it's highly unlikely that this was a "consumer" drone. (But there are definitely "professional" drones that have longer flight times)