I believe the main cause of the confusion was the US English V UK English of the Captain and International Aviation English for the Dutch pilot. With the use of non standard phraseology. "Lap and Land" etc.
The Airfield also appears to have been performance limited for their intended TOW. I guess cheaper to operate from Boeing field rather than SEA though. Both the TWR and Ground Controllers should have been aware of filed destination ATH. Why they thought they would want to make a Circuit and Land before departing for an 11 hour flight I do not know.