Sounds like a bit of slop in the chain. Sounds normal or it could be getting to the point the chain and associated parts need replacement.
There is also a small amount of slop in the position of the ATU on the D shape at the tip of the cam shaft. This need to be taken into account when timing the engine but once the timing is correct and the nut is tightened it can be forgotten about till the next time the ATU is taken loose.
The gears on the ends of the crank shaft and cam shaft are not loose enough that they can rotate.
Maybe what you are seeing is the ATU rotates a certain amount independent of the cam tip? This is how it Advances the timing. It is the advance Unit. As the rpm increases to ATU advances the moment the points are opened. With the ATU bolted in place on the tip of the cam shaft grab the top portion of the ATU and rotate. You can see the points cam underneath moving to open the points sooner. It is most properly called a "mechanical advance unit".