I was surprised that they would join without being able to ride first. I assumed the chap meant first canter on those horses, not first one ever!
Though doing it without stirrups looked great for their overall position, just not for any security. How many would have come off with the sitting trot.
The mounting puzzled me, but I wonder if this goes back to if you are injured you need to be able to get back on your horse? Though they don't actually use horses for war do they?