This is the mod in question: Cars Dump [MapEditor] - GTA5-Mods.com
I have seen that one (pretty sure it is that) in some FivePD Youtube (Jeff Favignano) vids, and wondered if anyone knows if it has been released as a normal YMAP or FiveM resource?
It is possible that they used MapBuilder to stream it - I have got MapBuilder working in FiveM but the mb_addons resource is ~700mb so it is quite a big resource to stream for just one map mod.