Inside a wind turbine during high winds - GIF

[Frank S]

Why on Earth would they be trying to assemble that thing in such horrible conditions? They certainly wouldn't operate it in that kind of weather.

The wind may have been dead calm at the beginning of the lift. This could just be a short period of gusts. The nacelle is already above the mounting point, the reason why the turbine tower is swaying is because of its surface area. no matter which direction the wind blows the cylinder is still going to be a huge sail in the wind. the lattice tower of the crane not as much by comparison. the Nacelle would rotate on the hook to present the least amount of wind exposure. At this point about all they can do is wait it out gusts of wind unless accompanied by storms or atmospheric pressure fronts are usually short lived. Once they do manage to stab the bolt holes with their bars or spuds the weight of the nacelle will have a dampening effect on the tower to an extent.
When we were installing some equipment on the Burj Khalifa we could feel that thing sway several meters on the 122nd floor while the big ugly skyscraper was still being built.