He is incapable of accepting the fact that the Titans' locations were moved around during post-production of GKOTM. These monitor images, which were from set visits conducted two years before the film hit theaters, show the monsters being in outdated locations and their appearances do not match those seen in the movie (where applicable). In the final movie they are deliberately barely visible, so the information displayed on them should not be taken seriously. Putting an image clearly labeled "LEVIATHAN" on the Kraken page for the sole reason that he is in the Indian Ocean is inaccurate. Just because Leviathan was planned to be located somewhere else instead of Loch Ness does not mean it's a different monster entirely. Depending on when the novelization was written, Kraken not have even existed at the time the movie was filmed.
Tl;dr, Leviathan is canonically in Loch Ness, and the monitor images should not be considered, period. Kraken is not Leviathan, and never appeared as an X-ray.