Is the Workflow module a Symfony component?
No, the Workflow module is not a Symfony component.

As for what you found, the first list are the Drupal core dependencies, which include its dependencies from Symfony components.
Under the replace section, you just find a list of Drupal core modules. You can understand they are modules because they are listed as drupal/&lt;module machine name&gt;, while the Workflow component would be listed as symfony/workflow.