Yes, exactly: the train's motion is caused by the locomotive. We are the train, and God is the locomotive. There needs to be a locomotive to move the train. The train cars by themselves can't move. Yet it is an error to look at the moving train cars linked together and ask what car is causing the locomotive to move.

Similarly, we don't cause our existence. We are contingent on our parents, on the oxygen we breathe, and on the food we eat. All those things are contingent on other things. There can't be infinite contingent things because nothing would have sufficient reason to exist; therefore, nothing would exist. But we do exist, so there must be something that exists necessarily, which does not depend on anything else for its existence. That's God.

By definition, God is not contingent on people creating gods. God would still exist if there were no people because he is sheer existence itself.

I tried to adapt St. Thomas Aquinas’s third-way argument to our context. Still, these classical arguments probably have better standalone explanations elsewhere than I can summarize here if you want to understand the rationale for believing in God.