Having given this a bit more thought I would like to retract my previous smart ass comment.
If the a/c flew North for 1 hour on the compass. If there was any wind the a/c will NOT be due North of home at this time. Therefore home will NOT be South at 180 & the Garmin should not read 180.
If there was no wind on the way out & he was actually due North, then the wind must have suddenly increased as he turned South, for the compass to read 210 would need a hell of a wind to need 30deg drift.
On the other hand.
If he flew North on the GPS for 1 hour then turning round, home WOULD read 180 on the GPS. And the compass could read whatever.
The question therefore is: Was the outbound flown on the wet compass or the GPS?
It certainly has buggerall to do with Lat nuts or transport drift nor Coriolis nor Isaac Newton.