Due to the very shallow turns, I would suspect they flew using airspace fixes only as a reference and much of the nav planning was done manually prior to the flight, using the FMC data for drift correction and not primary navigation control, although I suppose one could limit the bank angle using MCP or FMC. Of course, this would be a cinch to accomplish via coordinated ATC vectors.
Tannenbaum shape and the country of origin and flyover is quite fitting.