In situations like this, I say we just let the game itself be our guide. For example, the FT-86 G SPORTS Concept comes with sports tires, so I guess PD doesn't consider it a race car. On the other hand, concept cars like the Mazda Furai Concept comes with racing tires, so I interpret that to mean they consider it a race car.
But I can't use this car in Seasonal Events because PD doesn't consider it a Normal car. Just tried it on a 500pp Seasonal Event and it said I can't use this car. Now I can use the 86 GT Concept '09 in that same Season Event, But It really doesn't matter anyway.