I think throwaway40602 from the previous discussion had it right - there's a variable that clients can't normally set (dota_use_particle_fow) that allows seeing

I think throwaway40602 from the previous discussion had it right - there's a variable that clients can't normally set (dota_use_particle_fow) that allows seeing some particles/spells and allows guessing where the enemies are trough fog of war. You can even find open source implementations years back for this. It appears to be a popular feature in cheats. They probably just query the clients to see if it's set. Querying client cvars from the server is already built in the game engine. If true then the announcement just made it sound way more amazing than it is.