So, it seems other players are able to mount/fly vehicles that do not belong to them. 

Confirmed that they cannot loot fuel / inventory.  Players are not on team/clan/friends.

Relavent parts of config : 

"Prevent other players from mounting vehicle": false,
"Prevent mounting on driver's seat only": true,
"Prevent other players from looting fuel container and inventory": true,
"Prevent other players from pushing vehicles they do not own": true,
"Use Teams": true,
"Use Clans": false,
"Use Friends": false,

Oddly, when both prevent mounting options are set false -- non-owner can mount passenger seat, but not drivers seat.

Will look into this. Thanks for reporting.