Additional details:
X and Y agreed on C$100 per flight hour, including fuel and instructor. Both X and Y were Swiss nationals. ...
The Bern Appellate Court also found that X had pretended to be a properly trained flight instructor, while in fact he was not.
X denied that he acted as Y's flight instructor (who was an experienced pilot), but in the Supreme Court proceedings he failed to show that the Bern Appellate Court's finding was manifestly wrong.
Full background:
Seaplane pilot found guilty of manslaughter - Newsletters - International Law Office
One complication here, is that (as far as I know) in Canada one
does not have to be a CFI to provide seaplane instruction. Anyone with a Commercial license and seaplane rating may provide instruction and sign the basic endorsement. Additionally, ultralight pilots may fly on pontoons without needing formal lessons.
We don't know what certificates & ratings X held. If he had a Commercial license (but isn't a CFI) then whether or not he's a "qualified instructor" might be open for interpretation.