The distinction is important as a Topic is not the same as a Post. It is telling you you are about to create a new Topic (instead of simply Replying to an existing one). That’s crucial information.
Unlike a mere Post, your Topic:
- requires a Title
- will be listed on the Topic List.
It may also require
- a Category
- set of Tags.
You might find reviewing the nomenclature helpful:
In any case, you can customise the Text on your instance in Admin → Customize → Text if you so wish but I advise against confusing Users by conflating Posts with Topics. Discourse is opinionated about its naming convention.