I think it's just difficult direct translation or the previewers misunderstood... the 32 DLC cars are already available in SP and have been since day one (of each patch) without playing GTAO. So I guess it just means you don't have to download them now
They're not new or only just "now" available in SP.
If they're on the disc and in the regular 'car traffic memory' though maybe they'll spawn as regular cars now which would be new. Before they were only available for players in the garage. Never spawned in the game world.