Blitzer or something else?

Hello, an acquaintance has a question. He was 3 weeks ago on the highway. Unlimited, then 120, 100, then 80. He was probably at ”rolling out”, where 80 was, he was definitely too fast and from right came a light from under a bridge. As he had described it it was already pitch dark, there was a lot of traffic on the track and the light did not come from the front, but rather diagonally sideways, perhaps direction 2 o’clock, as he said. He was on the left lane and on the other lanes. the cars were on the road with very close distance. That is now 3 weeks ago. He ponders all the time, whether they flashed it, or the distance of the vehicles on the right or middle lane or whether this was a small construction site, which was equipped with red flashing light… He also could not see what was under the bridge. Since I am also interested in this, these mobile speed cameras can also measure distances and flash ? because as he explained it, it should be be very difficult to have flashed it, as there were cars to the right of it, which blocked the field of view to the Red Light. What do you say about it? If the right are on the strip, and should flash so obliquely, can the then reasonable photos and first quite realistic speeds measure ? Greeting Venschla