It's a hypothesis, and a working theory. Esta has by now gone through several of those, and lived out parts of his life where he was hurt for jumping to conclusions; and also, of course, hurt for having failed to come up with any theories at all.
He has found no better answer -- nor do the more senior clerics teach it -- but to go on thinking, and be ready to step back.
Esta does pay attention to the actual content of what Merrin is saying. Reality or game, you have no choice but to play it either way.