Edit2: Maybe your post is mostly ironic and you're already fully aware of the issue, but I leave my post for any other readers that do not.
You can configure basically any kind of algorithm to output a nice looking return in-sample. Literally, you optimize the seed of a pseudo random number generator or a hashing algorithm to do that. It does not imply that it works out-of-sample. Not working in-sample does suggest not working out of sample (but is not a binary implication since it depends on what you have in-sample).
An interesting case I observed was on a site where people submitted Python codes/bots to play Rock-Paper-Scissors. One of the best performing bots was a few characters long as just calling a particular MD5 hash of the sequence of moves observed thus far. It turned out the guy that wrote it had downloaded all bots and checked which particular MD5 hash output (when transformed into an output move) would win against all deterministic bots. Against the best bots incorporating randomness it still loses almost every time though (and has 50% win rate against lesser ones).