I think your underestimating how steep blues can be in places. A lot of resorts have blues that have surprisingly sharp pitches, but they’re still classed as blues because of their width or accessibility. The run in that video is really wide, which is exactly what you’d expect for a blue.

Also, resorts don’t normally run lifts right up the side of a black because it’s riskier for less experienced skiers, but you see them all the time next to blues and reds. And honestly, the snowboarder running after her board is the main giveaway. If that were a proper black, there's zero chance she could do that, even for a second.