Hi, good job on the canelés. Yours do seem denser than what seems typical, though the outside looks like the right color. It looks like the Seriouseats recipe photos also show a more open structure. I've bought them many times and made them a few times, but with copper molds, and posted about it while back. You can check my pics and recipe for comparison if you want, though the difference in molds may result in different outcomes. https://www.reddit.com/r/Baking/comments/5wjnn5/canel%C3%A9/
Some ideas - Did you weigh your ingredients? Was the confectioner's sugar a poorly controlled variable in terms of corn starch inclusion? Was the oven thoroughly preheated?
I also see that the one in the cross section pic looks to have sunken in quite a bit on the sides compared to the one in the pic showing the exterior. Did that happen as they cooled? Was it cut before or after it cooled? It might be a clue of some sort, but it's hard to say.