I had the same skill (still do). Imagine following the instructions the first time. A part you're encountering for the first time stimulates the memory. I knew my collection like a dragon's hoard. For instance, I owned twelve white 1x2 tiles, all from Coast Guard Station, so that was the limiting piece when building tiny space-fighters...
> My kids have a photographic memory
How do you know it is photographic memory? More than one of your kids have it? Do you know why or what may have contributed to its development?
Read the whole sentence- this is clearly an informal use of 'photographic memory' to indicate that his kids are really into Lego and keep track of details in the way only kids can.
I didn't see him making any generalized claim. I recall the things I'm really into better than I do things I'm not, which is all I think he was saying about his kids. (My four year old remembers facts about volcanos - including the name of the scientist who made the claim - waaay better than he does where he left his shoes, so it tracks for me!)