If you look at the C&M website and how the search criteria is performed you'd notice that there are a myriad of options for flight crew, eg co-pilot, pilot, first officer, second officer etc.
It seems to me when C&M get a new role to advertise, they'll put it under the flight crew categories it best applies to. Since Flight crew encompasses all of the above options, it's possible to find this role under "third officer". A closer inspection of the actual role reveals that it's a First Officer role.
Nothing complicated here as far as I'm concerned.