He has to be pretty confident jumping into a half when a lot of eyes are watching, especially those wanting to say, "I told you so". Based off his training, I don't see him going out there and breaking 64:00 on his first real attempt. He has done really impressive things in the ultra world, but sub 4:55s for 13.1 miles is so far removed from the paces he has run tens of thousands of miles at.
I see this as him testing the waters a bit to see if he can go out there and run a sub 2:19. If he can run 65-66, he should have no problem running an OTQ a month or two later with some "real" marathon training.