the console command does not wrk as the OPEN command is used to open a server or server browser.... mayby its summon but summon wot?

Instead you could doubleclick the vehicledemo.ut2 file in the maps dir... someone saw this file and did the "open vehicledemo" console command instead of telling that it's just a regular map, to look l337??? if you rename it to DM-Vehicledemo.ut2, you'd propably be able to play it as a regualr deathmatch.