What causes "cam walk"?

It doesn’t sound like they had it set up improperly……unless there was enough forwards thrust force to bend the timing cover outward(it can happen), then the .005” thrust clearance you had set, ends up being more.
You should use either a pretty rigid timing cover, or have it so the timing cover is nearly touching the back of the water pump.

As for your original question:

How to Prevent Roller Cam Walk

What forum was that discussion on?