That's correct. You are only paying for the cost of the Warehouse. So 1 user asking 100 questions and 100 users asking 1 question each are the same, assuming all of those questions kept the same clusters on the same WH 'up' the same time.
The "limits" are mentioned here:
https://docs.databricks.com/aws/en/genie/set-up#technical-requirements-and-limits
So this is considered "free" from the perspective of tokens to the LLM.
There have been requests from customers for higher/guaranteed QPM. Those may be priced in future.
But in reality we have found (based on telemetry) that most customers very rarely hit even the current "free" limits.