Looking back at the videos, a lot of it is in cloudy or partial sun conditions, so not super bright sun. In this shot from over the city, it looks like if anything the light is straight up overhead. Note most of the sphere is in shadows and the brightest roof on the buildings are those that are horizontal. Yes they are probably a more reflective material. What shadows we can see, like on the buildings directly below the sphere appear on the upper 1/3 of the right side as seen in the picture. Even then, it's not much of a shadow, suggesting soft or filtered sunlight:
View attachment 81472
If anything the whole scene looks washed out, possibly from cloud cover, which is clearly present earlier in the video, compression and possible post production adjustments.
In any case, there are lots of styles of fishing line like standard monofilament, fluorocarbon and braided, all of which have different reflective properties. A little experimenting would show the best to use in this situation.
Let's also remember, we're only presented with what the German Company wants to present. These are all edited presentations of selected scenes. It may be very likely the fishing line occasionally showed up in a scene, so they just don't include that. We're not seeing a collection of raw footage, we're seeing a staged event.