Given how abruptly it ends, and the fact that this "chapter" is so short compared to the others, it's likely that this isn't intended as the ending of the story or even as the ending of chapter 11. Since Imitation Crystal has freedom in how they release Goldfish Kingdom (it's a free manga hosted on their own website), they don't release chapters all at once and instead add individual pages to a chapter over a stretch of time. You can verify this by looking at old Goldfish Kingdom webpages on the Internet Archive.
My guess is that Imitation Crystal hit some creative block midway through chapter 11 and never got around to finishing it. Even though it's been 6 years since the last update, I really do hope they return to Goldfish Kingdom sometime soon...