Questions about motorbike gearbox

I just came across this video about a motorbike gearbox, and have a couple questions.

Firstly, she says the detent for neutral is between first and second gears. Why isn't it between fifth and first? That would seem to make more sense to me. Are you expected to shift down to first when setting off, then shift back over neutral to get to second? And presumably the grooves in the shifting drum have gaps between fifth and first to stop you shifting too high and ending up back in first, or is there another mechanism for that?

Secondly, and probably more importantly for my understanding of the transmission, can someone elaborate on how the 'constant mesh' transmission means it doesn't need synchronisers? For example, before the shift from neutral to first is shown, the input shaft, and the first free-wheeling gear with it, are rotating while the output shaft and the corresponding dog clutch are not. Surely, when the dog clutch is moved to connect with the free-wheeling gear, they wouldn't be able to mesh, unless it happened right when the recess and pin were in line, and even then that would cause a jolt. What am I missing here? I also watched another video with a physical gearbox, which seems to confirm that it works like in the first video, but doesn't explain it much, and I can't really see why it works.