Muskets were innaccurate as fuck, but not as much as some people claim them to be.
I can't view that video on my phone, so I'll watch it when I get home. But it is probably a skilled shooter. Them being innaccurate wasn't the only thing that made you miss, psychological shit had a huge impact. That guy/girl in the video needs to do it while under fire from enemies with the same weapons, in a line, with people dying and limbs flying off to the left and right of him/her.