Generally good advice, but may not be that simple.
A couple of unknowns here - was the instructor with a shop, or an independent? If with a shop, was he an owner or an employee? That may influence the course of action you choose to take.
I generally agree with trying not to create conflict by taking a measured approach. But if you reach out to the shop first and don't come away with a pretty solid gut feeling that the situation will be addressed, then move on to the phone call right away rather than waiting to see if anything has changed through observation. If, heaven forbid, something happens in the future that could have been avoided by a timely communication today, will you wish you had taken a different action.
And PADI is not overly quick to drop their members. They have a pretty solid process for investigating a report, making sure they get the facts right, and then determining how to remediate training for a member as needed rather than just leaping to significant consequences. So it's not like reporting the issue will get him "fired" from PADI.