And if he's concerned about the moisture from below traveling up into
the wood, then I would never use oil based in that application. Oil
based forms a less permeable surface and won't allow the moisture from
the wood to escape like latex will. The result can be peeling. I
also would never mix oil and latex coats on a job either. IMO, two
coats of the same product should have been used on this job.

I agree that the best thing to do now is figure out what was used if
you can. Then go to a good paint store and ask them for advice on how
to proceed. It sounds like the only logical approach is going to be to
remove what's there and start all over. If you're lucky and it's
really loose, most of it may come off with a pressure washer. You need
to be careful not to use too much pressure and screw up the wood
surface though.