Authorities found the smoke originated from a Samsung tablet wedged between two seats. It had been left behind by a previous passenger.
While the US Federal Aviation Administration had recently banned the inflight use of the Samsung Galaxy Note 7 due to its potential to overheat and explode, Samsung said in a statement that the device was not a Note 7.
"It appears that external factors contributed to this incident," the spokesperson told the Telegraph. "This is not related to the Galaxy Note 7. We have reached out to Delta to investigate as the cause is yet to be determined."
Several airlines, including British Airways, Qantas and Cathay Pacific, have warned passengers not to retrieve their phone if it gets lost on board, but to notify a staff member instead. When electronic devices get caught in the mechanics of an airline seat, there is potential for combustion.
In May, a smartphone started smoking after being wedged between seats on a Qantas flight from Sydney to Dallas. The phone was placed in a jug of water and sealed in a metal box, with no diversions required.
A similar incident happened a month later, when a smartphone was crushed by the reclining mechanism of a seat and exploded into flames during a Qantas flight from Sydney to Los Angeles.
Crew used a fire extinguisher to put out the blaze and the flight continued on to Los Angeles.