I wouldn't worry too much about it. Ive had a very similar thing happen with a small company a couple years ago - I submitted the verified correct solution and

I wouldn't worry too much about it. Ive had a very similar thing happen with a small company a couple years ago - I submitted the verified correct solution and got a rejection letter to not come in for an in-person because I didn't style my code according to some BS guideline they use internally but didn't elude to in the instructions. I honestly was happy that I wasn't selected. I can't imagine how many decent candidates they pass up if it is their normal operation. I'd much rather work for a place focused on solutions rather than coding style (I've been at a place where people argued over curly brackets all day - its horrifying especially when funding gets tight). Funnily enough, I was browsing jobs about 6 months back and that small company still has the same job opening available a year and a half later.