Looks like one of the largest diameter Ti tubing ever used on a bike, so it'll be plenty stiff. The rigidity of a tube is a function to the 4th power (^4) of the diameter. So just a slight increase in diameter can result in twice the stiffness. Then remove some material from the inside to restore stiffness back to previous levels and you've got the weight-savings.

Also the orientation of the ovalized tubing results in increase stiffness in certain directions. Notice that the major axis of the tubing at the bottom of the seat-tube and down-tube is aimed laterally? This definitely will reduce lateral deflection of the bottom bracket under pedaling forces.