What are the differences between a tomcat thread and a thread started by the async annotation in spring boot?

Question

I'm learning about threads and how threads work when building a web application.

As per my understanding the flow is as follows:

1. User sends Http request
2. Tomcat creates a thread running the controller.
3. Spring boot runs an async annotated method, that runs code on a seperate thread pool created by the spring boot app.
4. The tomcat thread is released until the async method is completed to handle more requests.

Am I correct in my understanding?

Does spring boot create its own thread pool to run async operations on freeing the main tomcat thread?