The "invent" is similar to "forge", but it didn't say tell (qala) a lie regarding God, but forges/fabricates a lie. You have to keep in mind the context that Mohammad (s) is accused as forging a lie against God.
Oh, c'mon! That's just a ridiculous exercise in semantics.
The word "Aftara" is a bit stronger, in that, it means you go out of your way to attribute to God. An example is regarding halal and haram. If a person is mistaken, it's not treated as forging a lie attributed to God, but if you are a scholar and you attribute halal and haram without knowledge, it's treated as forging a lie.
It's subtle, but there is a difference.
It is clearly referring to those who reject Islam by not accepting that the Qur'an is a direct communication from Allah. That's the "lie", and you know it.