It depends on which one you take. Side with the younger one, and it's very subtle. If you side with the older one, however, he drops into Cory's backward grammar while talking to you. It's still pretty subtle, but it's a lot easier to see.

Personally, I don't see it as an idiot ball thing. It is subtle, and Hawke had no reason to expect it - he didn't know the secret of the Wardens (and I doubt Anders or the young Hawke would, either) and this wasn't an "old god" in any event. What bothers me is that, again, your choices have limited impact on the outcome, and either way there's a new wildcard on the table that nobody is aware of.