Yes. What the AutoFormat As You Type option does is apply Heading Styles to your text. That is a paragraph style. You may want to create a paragraph style in your document that is based on your Normal style or Body Text Style and has bold formatting.

Then user Replace (Ctrl-H) to replace the heading style with your new style. If you have no paragraphs you want in the heading style, you can simply replace it using Replace All. Otherwise you'll want to step through them using Find Next.

To get to the Styles in the Replace dialog, you'll need to use the More button. Then Format and Styles. Note that your cursor has to be in the Find box when you put in the Heading style and in the Replace box when you put in your style.

Understanding Styles in Microsoft Word

The reason this happened is that the heading styles come with an outline level as part of the style. That is what is showing up in the Navigation Pane.

You may also want to look at some of the other reasons for using these styles.
Why use Microsoft Word’s built-in heading styles?