Not necessarily. A combination of specific blood tests at the time, witness accounts of how the person behaved during and after, any video of the event, EEGs and brain scans could make it more or less likely.
It seems as if witness accounts are definitely missing and I think I remember that witnesses have suggested the driver didn't behave in a typical 'post seizure' way.
However the driver may have provided appropriate medical evidence and/or the police decided there was no way they could prove anything beyond reasonable doubt.