My first reaction is that this is a misuse of the term "procedural memory." Procedural memory means any "how" knowledge. It includes how to ride a bike, how to twist a jar lid the correct direction to put it on vs. take it off, how to play the piano, how to hit a baseball, . . . well, you get the idea.
In absence of any other evidence of a disorder, I would say they've found that he has a problem with . . . doing math on paper. Period. Maybe the pencil-and-paper techniques just haven't "clicked" for him so he's always done the problems in his head. Maybe he just needs extra instruction in the specific techniques.
But further testing might show that he does have a broader problem. For instance, does he have problems with reading symbols? Or seeing that things line up in a column?
But without that extra evidence, I would say that calling this a problem with "procedural memory," or any other broader thing, is just not warranted.
