The problem is holding position, not endurance
It seems obvious that this is a test for a long endurance UAV where they put in a pilot during the test phase as they need the flexibility that a pilot gives during development.
This I buy.
However, I am not sure it will be able to remain circling around one point for a long time if the wind gets up. If you can only go 44mph, and the wind is > 44mph, you will start to drift off.
What they need is more power, and hence solar cells that are more efficient for the same mass (check out their website). They would also like better batteries (as would the whole EV world).
They may be in luck with the batteries as loads of people are working on this, it is likely to happen sooner or later. The solar cells are another matter. Lots of people are working on solar cells, but I have not heard of anyone working on very LIGHT ones. This they will have to pioneer themselves.
Then there is the ultimate efficiency of solar cells. These seem to top out at about 38% at present for very expensive ones. They are using 12% ones (for lightness), and we could imagine they could get to say 18% with a little work.
This is still only 50% more power, which might allow them fly 25% faster - say 55mph - this is still too slow to hold position in many stratospheric zones.