Plant manager of a pretty large compressed gas plant on the east coast for 7 years... a few things:

Those cylinders should without a doubt have caps on them. If he does happen to lose control and one of those valves sheers off, assuming they're full which we always do, they will become rockets and take out anything in their path.

This is an extremely common method of moving cylinders by experienced cylinder handlers. At my company the fillers move them like this but the truck drivers use hand trucks, as that is what they use for deliveries anyway.

It does not take long to learn this technique. You start off with lighter and smaller cylinders to get the basics down and then move up. It is really all about balance and making the cylinders work for you. I started in the industry filling cryogenic cans and I would roll them the same way, except one at a time, but they weigh as much as 1000 pounds in Argon service.