On this hand, GIB responded (and explained his response) as I would have expected. Since his 1N bid showed 8-11HCP, I'd expect him to decline the invitation (i.e, pass) with 8-9HCP and accept the invitation with 10-11HCP, or something very close to that. Here, GIB accepts with his max, and the explanation of his 6N is what I expected.
Here, North's 3N shows 12-19HCP (I'm guestimating the 12, based on GIB's fairly-consistent use of 1-point difference between HCP and total points.) Therefore, when I make a quantitative 4N bid, I expect GIB to decline the invitation (i.e, pass) with 12-15HCP and accept the invitation with 16-19HCP, or something close to that. Here, GIB accepts with a min, and the explanation of his 6N is consistent with this surprising bid. Why would 6N show 12-16HCP instead of the upper-end of his range?