It has been my experience, with customers having seizures in the store ... that they will not transport, an unstable seizure patient.
They call the hospital, which usually gives authority to give Valium IV, and monitor for a short time. The major risk with seizures is
to the head (from the fall), and breathing if a status one develops.
In the ambulance they will give oxygen, and watch the vitals.
They probably sent EKG tracings too while waiting to leave. Once they see the Valium is taking effect, then they get permission to transport. If the drive is long, that may be a factor too.

He could have had a stroke of some kind, that caused the seizure.
Brain tumors also have that potential, when they become big enough to set off a seizure. Ted Kennedy's seizures were his first warning of his brain tumor.

Sounds like a very alarming situation all around. I hope the wife is okay?