Well, the cognitive skill he has that is both strong and strongly associated with math is his working memory, so that part of the equation adds up. And BD, which is visual spatial, has some connection to geometric and logical thinking too, depending on how people solve the puzzles.

Also, on both the WISC and KTEA, the timed tasks that scored well are all oral only. So it's probably not processing speed per se that's the issue, but only certain types of speed (fine motor, rapid naming).

...pronounced like the long vowel and first letter of the alphabet...