As far as I know ambassador have a total different role compared to the European Commission.

They sure do, but that's not the point I'm trying to make. We tend to call someone that is elected by the people 'elected'. Someone who gets decided on by these elected representatives we call appointed, they don't inherit the 'elected' attribute. If they did, essentially all political officers (e.g. high level workers in a government department) would be elected, because they were chosen by elected officials.

US supreme court judges get nominated and confirmed. The president is elected (well, kind of, but most agree that he/she is elected by the people even though the electoral college is mixed in there) and then nominates a judge and the Senate confirms the nomination. I don't think it's common to call the supreme court judges 'elected' though, despite their selection by two elected parties.