The payer is required to issue a some type of 1099 if they pay you more than $600 in a year. Giving you the W-9 to fill out now is a good practice for them because they may not know which of their reviewers will cross that $600 threshold, and if they wait until you cross the $600 threshold to send you the W-9, they can get in trouble. Sending you a W-9 does not necessarily indicate that they will issue a 1099 and it does not indicate what kind of 1099 they will issue.
If the payer classified it as hobby income they would report it on a form 1099–MISC, and if they consider it self-employment income they will use a 1099-NEC. Which form they use is not an ironclad proof of the type of income, but if they use a 1099-NEC, it creates a strong presumption at the IRS that this is self-employment income.
again, the difference between hobby income and self-employment income is that self-employment income is generated from “an ongoing trade or business.“ If you believe this is a hobby, and the payer uses a form 1099-NEC, you can still report it as hobby income, but you should expect that the IRS will send a letter asking you to prove this or else pay self-employment tax.
