You didn't do anything wrong! It's just that if you consider two principles: (1) frontpage space is by far the scarcest resource HN has; and (2) repetition isn't good for curiosity, it follows that we need to try to keep a fair amount of time and space between similar-ish topics.
It's also in the interest of the follow-up post because then community interest in that-type-of-thing can focus on it specifically instead of getting split between semantically-overlapping threads.