I expect they're probably using a variety of 7075 Aluminium alloy (Aluminum for the FREEDOM!!!!! folk) which has a slightly higher thermal expansion then a lot of steels. But even so, I've seen it used as components in jet turbine housings and mounts and it sure didn't get anywhere near 13mm of expansion while in use, nevermind on a hot summer day.
I suppose they could be talking about total expansion by volume as opposed to directional. Would be a daft way to phrase it though.