They've clearly got the set-up of the forms into a pretty efficient rhythm as this got done in under a day. With this amount of concrete, you really don't need that support, but on bigger jobs, man you better make those forms sturdy! You hear tales of one-inch thick sheets of plywood just splitting apart down the middle like a zipper with concrete pouring out of it as not enough whaler bars were put in place.
Hmm, some of those forms don't look perfectly vertical to me. Tight sphincter, people! I'm still too young, but in about twenty years when I'm truly an annoying old codger, if I'm ever in a similar situation, I'm going to hang around while the guys are working, constantly checking their work and making sure they do a proper job. That's what the old portuguese guys did and I bet they got better quality sidewalks than we did!
See the vapour barrier/insulation to prevent water from getting down there freezing and causing cracking
Bring on the cream!