FedEx dont operate the 767 (yet) and the '57 doesn't go to DUB. It would have been a PW powered A300-600. If the engines were cold soaked it's a common characteristic of the PW4000. The PW powered MD-11 does it as well. As the aircraft sits over time the bearing seals lose air pressure and allow oil to seep into the engine or transfer across the seal during inital high oil pressure on start. It also has a generous fuel schedule on start so theres probably a bit of unburnt fuel in there too! Sometimes on the MD-11 after a 50hr+ layover you cant see to push the thing back initially when #3 lights up!