"There was smoke seen by a crew member in an oven so the captain made the right decision and decided to come back to Sydney to check it out as a safety precaution," Foster told The Associated Press.
"They had to dump fuel because it's a very heavy airplane with 15 hours worth of fuel to get to Canada," Foster said.
She denied earlier reports of a fire breaking out on board.
"There was no fire at all," she said.
There was no damage to the Boeing 777 and no smoke entered the cabin, Foster said. Engineers who examined the plane determined a faulty oven caused the smoke and removed the appliance, she said.
The flight, which was bound for Vancouver and Toronto, returned to the air later Thursday afternoon.
Australian air safety investigators said they don't plan to investigate the incident.