If he struck him twice, I would think it would count as two hits, from what I can remember.
Quick tip (not sure if you know or not): but you can just get the Black Star and make your weapons have two enchantments, one being soul trap. So every hit you take, you will have a soul no matter what. Unlimited. Your weapon will never run out. You will also not have to carry any other soul gems. Also, this allows you to make your weapon as powerfully enchanted as you can without having to worry about having enough to recharge constantly.
I could be wrong here, but I think these are separate entities. The black star would make sure that you can always come by an easy grand soul (bandits) when you need one. To dual enchant requires not the black star, but an enchanting level of 100 and the "twin souls" perk, and there is a separate perk (soul siphon) in the enchanting tree, which allows your weapon to partially recharge with attacks on beasts only.
Giga's right about the black star, in the sense that it's essentially free soul shopping, because you can't really walk Skyrim without being attacked by somebody.