That scale has always been considered extremely generous... in fact, there is rarely a score posted below 6.5 or 7. We have always found PG events to be very well run and scoring to be pretty accurate (from a relativity standpoint, not as it relates to that scale). But we have been removed from that scene for some time and I am not surprised to hear some experiences that are not as positive, considering their recent growth initiatives and shift in focus.
The scores have always been less reliable for the very young. PG has stated that projection is a big part of the analysis. So, my guess would be that the OP son didn't score great because he already has a big body and his arm strength hasn't yet matched his growth - pretty important when projecting a C. Giff, I am also curious... that is a big 14 y.o. catcher... how is his agility behind the dish? Usually, a kid that age, that size, is dealing with some awkward growing into his body and not really "nimble". Similarly, with hitting, does he show good over-the-top pop yet? Does his swing show proper mechanics and compactness that will allow for him to hit college pitching yet or is it still a bit gangly?
Sounds like he has good size, good work ethic and great resource in an experienced dad to help him stay on track. If I had to guess, he is well on his way, just needs to grow into his body and get closer to maturation. If he keeps growing, I wonder if he will remain a C?