You most likely entered a 1099-MISC that is being classified as self-employment income. Whenever you enter any self-employment income, TurboTax will create a Schedule C and ask you for information to create your business profile. See the IRS links below for further clarification.
Another way this can happen is if you entered a W-2 and checked box 13 for a ''statutory employee''.
Who is Self-Employed?
Generally, you are self-employed if any of the following apply to you: