I don't know, the tripod collar on this image seems to match the 100-400's collar (check out the tightening knob), but the 70-300's collar doesn't seem to match up:After consulting the pics on the B&H web site, the lens is the 70-300 L. It definitely is not the 100-400. I have one beside me bolted to an R. The zoom ring is longer on the 100-400 otherwise it and the 70-300 are arranged similarly and there is the step down in diameter after the tripod mount.
It seems the camera pictured here does not have the plastic dome or roof over the pentaprism to house the gps and wireless antennas which shows prominently on B&H's 1DXiii photos. Perhaps that roof fell victim to a hurricane or Photoshop.
70-300 tripod collar https://www.bhphotovideo.com/c/product/747346-REG/Canon_4429B001_Canon_Tripod_Mount_Ring.html