One thing I worry about is if you have a lot of shrinkage, it's often because of a lot of material. So simply applying more isn't a good fix. Not without "opening" that up by sanding it for paint and leaving it breath a while, a few days. Then scuff it down and re-shoot it.
It's so hard to say without being there, the guy may be right on the money and there were just some coarser scratches that were missed and the paint you applied couldn't fill them and it simply needs to be redone. But I have seen guys apply so much material that was full of trapped solvent it needed to be opened up and sat in 100 degree weather for a week before being re-shot as it was still flashing off solvents all that time, it was FULL of solvents.
And applying something "heavy" doesn't necessarily mean too many coats or something like that, applying it with too slow a gun movement, too slow a reducer for the metal temp, too many coats, not enough time between coats, there are lots of ways you can apply it "too heavy".
Just be careful because applying more over something that is full of solvents isn't the way to go.