I'm sure they mistyped '6' over '3' from numpad; it can happen to any of us.
While I find your explanation plausible, who has the muscle memory to press "g", "c", "c", spacebar, lift hand to numpad, "1", "6(no 3 sire!)", hand back to home row?
It's faster for me than looking down to figure out where the numbers are on the top row
If you used the top row more often, you wouldn't need to look down...
To be fair, you can be typing "gcc" with the left hand, while the right hand moves to the numpad.