Chaps, you are mixing apples and pears here. The FAA PPL has nothing whatsoever to do with any microlight, UK-based or otherwise, that Sam's friend may or may not be flying.
If he holds a standalone FAA PPL he is good to go day VFR in any G-reg,
AFAIK worldwide.
The only uncertainty at this point in time is the EASA threat to FCL, well documented in two other threads here.