Far too often we see lasers from the business end (inside or pointing into the sky) and frankly they all look alike in my opinion no matter at what mW. It's much more interesting to see how any particular laser appears when looking at one from a great distance.
This doesn't surprise me as I thought the link to the pseudoscience mapping the earth as flat was flawed in that a three watt couldn't be located at three miles out. This doesn't seem to be done with binoculars or a telescope either, just a camera. If they wanted to modulate the beam with audio, it could be used as a line of sight transmitter/receiver.
Nice experiment for sure, though it doesn't really state anything about what was used on the transmitting side - just a simple 532 handheld, or perhaps something with a beam enhancer?
Getting the line of sight path for 25 km is not that difficult - you need to be about 50 meters above ambient ground/sea level to achieve it, so it could be replicated from any highrise really.
It does get more difficult after that though, to achieve 50 km you need 200 meters elevation, and for 100 km about 800 meters and so on. Given that the limit would be in the order of 300 kilometers if you stood atop mount everest and had a clear path to sea level (not likely given weather and height of surrounding land).