It seems ridiculous to me that someone joining the site to post a riddle they've created would get their question closed until such time as they say explicitly that they've made it themselves. It also feels somewhat unfair, since it holds people to different standards: I'm sure that if it was me posting a riddle without saying explicitly that I'd made it myself, nobody would vote to close it because you all know that I write my own riddles.
(In fact, the whole attribution policy doesn't make sense to me, especially in cases like this where the puzzle consists of just text rather than a screenshot from somewhere. If the OP had taken their puzzle from somewhere, they could just lie and say they made it themselves. A policy that relies on honesty in unprovable cases doesn't feel very consistent. But I digress: the policy was created through meta consensus and it's an official close reason, so there's not much to do about that.)
Can we please be a bit more careful about closing people's questions when there's no reason to think it might be copied without attribution? If it's an obvious screenshot from an online IQ test or something, then sure, close away. But if someone posts a riddle like this, why would you presume guilt rather than innocence, when people have been posting home-made riddles on this site since 2014?
I'm not necessarily advocating any change in the attribution policy itself, just would like to ask people to be a bit more careful when casting votes on new puzzles. A lot of people post home-made puzzles without seeing the need to say explicitly that they're home-made, and we can't reasonably close every such puzzle.
(And yes, I know that this question will get quickly reopened now that the OP has said they made the riddle themselves. But my point is that it shouldn't have been closed in the first place. What happened to benefit of the doubt?)