The felon doesn't have to cross state lines, just the firearm or ammo. So, unless the firearm and ammo were both manufactuered in the same state where the felon possessed them, "C" is automatically met. Chances are the case just wasn't presented to the feds.
This is 100% correct. Element C is the jurisdictional element for this to be a federal offense; Congress gets its legislative authority for (most) criminal offenses from the commerce clause of the constitution, which requires a nexus between the action and interstate commerce. In most cases (this one included), it’s pro forma but still has to be proven.
Also, I don’t see any 10 year minimum associated with 18 U.S.C. § 922(g). There is a 10 year maximum. (there is a 15 year minimum it the person has 3 or more convictions for felon in possession or certain drug offenses.