You have self-employment income if you are "engaged in a trade or business." Although the concept of being engaged in a trade is a bit murky, it usually entails things like an attempt to make a profit, maybe advertising, maybe maintaining inventory or keeping a schedule, or doing other things that a regular business does.
It would seem safe to declare this as hobby income. That means that you can't deduct related expenses, such as tools or mileage. But it sounds like you really aren't interested in doing that anyway.