That's the first thing I thought of when I heard about this. If the US was testing its drones, I think it would prefer to keep them in a restricted airspace. On the other hand, if I were a foreign power looking to flaunt my new drone tech, I'd take it over the area that seems to be rife with sensitive bases.
Still, it's most likely this is a US drone on a long range testing mission(or just flying off course due to a sw bug).
For hypersonic vehicles, restricted airspace is too small. They need to be able to fly into commercial airspace to demonstrate range, guidance systems, etc...
Are there reports of any foreign drones flying so far within US borders? I only recall media accounts of stuff like that happening in international waters or borders.
Still, it's most likely this is a US drone on a long range testing mission(or just flying off course due to a sw bug).