There is nothing wrong with posting a new answer to a question if you can provide new or additional information. In fact, I would say that this is good form—a diversity of solutions to a problem is welcome. Obviously you don't want to duplicate information that has already been provided in another answer, but if you have something fresh or original to contribute, you should not hesitate to post an answer of your own—even if an answer has already been posted and accepted.
Of course, if your "answer" doesn't actually answer the question, and instead just provides useful interesting or related information, you probably shouldn't post it as an answer. Instead, just post a comment to the question. Answers should be reserved for things that actually answer the question.
Finally (and I suspect this is the reason someone downvoted the specific answer you link to), answers should be more than just a link. If it's a link to an external site, you should reproduce enough of the information found in the linked page to make your answer self-contained. This is particularly important to stave off link rot, but also important in our journey to make Stack Overflow a self-contained resource and repository of information. If it's a link to another question/answer on Stack Overflow, that should definitely left as a comment. Those don't amount to an answer to the question, and the question might even need to be closed as a duplicate.
I think the answer you left should have been a comment:
By the way, I wrote my own Minesweeper game a few weeks ago, and needed to know how to click both mouse buttons at the name time on a number to unveil all the covered boxes surrounding it. I asked an SO question about it; you might find the answers useful.
But I would definitely encourage you to continue posting such helpful comments in the future! I do this frequently. Even the person who asked the question thought it was helpful, commenting:
Cool, that might come in handy