It means the seller actually has the ownership document for it. For some reason in the off-road world, ownership documents go missing/lost/never registered, etc. Annoying, b/c you'll need it to get a green plate if that's the plan (will need it for insurance to legally ride Ganny, Simcoe Forest, etc).
Extra hoops to jump through with MTO if you don't have an ownership and want to get one. Lots are sold without ownership every day, just depends on what your plan is with the bike.