No it’s atheism. Lack of believing. Some atheists take that to a near religious level, believing very fervently that there is no God. But most simply don’t believe in God. There’s an important difference between active belief in a lack (which I like to call anti-theism), and merely lack of belief (actual atheism). Most atheists, having opted out of belief, then move on with their lives, it’s not a big deal one way or the other.
Agnosticism is VASTLY different than you portray. Agnosticism says there’s probably something but we haven’t figured it out yet.
The big difference shows up in the thought experiment of what happens if God knocked on your door and said “hi”, in a very literal no interpretations necessary sense. An agnostic would now have the answer and know what to worship and how. An atheist still wouldn’t worship, because he’s not a worshiping kind of guy.
Your thought experiment contradicts your assertion that atheism is “merely lack of belief.” If God literally knocked on an atheists door and said hi, then there would be extremely strong evidence for the existence of God. However, despite this evidence, the atheist would continue to posit that there is no God. It isn’t a lack of belief, but instead a belief that there is no God.
I think the distinction you’re making is between faith and theology. You can have faith in various things but still not believe in the supernatural.