Pitts - yes really, surely you'll agree?
"3,100 m, the temperature was -5° C, the dew point was -5° C" - is not icing conditions.
Most of his flight was in crystal blue bone dry air, with a shallow presence of colder moister air below him - but no indication of flying IN icing conditions - it might be a red herring.
Just because FZFG is present at some locations does not mean he was in it.