Well, he doesn't think the route suits him. Again; wouldn't he be the best judge of that?
And the other part was regarding the argument that he should (have) skipped the Vuelta instead. However, the Vuelta gave him several chances for success - he's already had it - while the World Championship would have just been one, that could just as easily have failed.
To the first part: No. It's just a bad excuse.
Winning the WCRR is much more significant than anything he could do in the Vuelta. But sure, less likely. But by a similar logic that would mean that classics specialists with a decent sprint should pick Itzulia because they're more likely to win a stage or to there than winning Flanders or Roubaix because the competition is less. Fortunately, that's not how cycling usually works.