This study doesn't establish that an odor precedes a seizure. They took the samples from someone who was in the middle of a seizure or shortly afterwards.
This study doesn't establish that, no. But there is considerable anecdotal evidence of service animals that can alert well in advance of a seizure, before the patient is aware of any prodromal symptoms.
That's interesting but how do we know it due to smell rather than sound or other senses? I've read that dogs and other animals can also anticipate earthquakes because they can hear or feel the earthquake earlier than humans.
(For example: https://news.ycombinator.com/item?id=19522755)