You're right, the answer was definitely problematic. But the message the moderator who declined your flag seems self-explanatory enough:
flags should only be used to make moderators aware of content that requires their intervention
Think about it this way: what did you want a moderator to do with that answer? Now, which of those things could you not have done yourself? Here's my list:
- Edit the answer to fix the link
- Edit the answer to remove the link
- Edit the answer to include a summary of the solution
- Leave a comment suggesting that the poster further develop the answer, including a summary of the content from the linked page within the body of his/her answer
- Delete the answer outright
The only oneNow, how many of those things that you could not doyou have done yourself? The only one that you couldn't (i.e., the only one of those things that requires the attention of a moderator) is deleting the answer.
And while sometimes that is merited, I hardly think it is appropriate for a self-answer posted a mere 14 hours ago (perhaps even a shorter time ago when you first submitted the flag) by a new user. At least give them time to fix the problem, or help them out by fixing it yourself.
If and when those strategies fail, and if the answer is still useless, then you can flag it and ask a moderator to delete it. I doubt they'll decline that flag. If you want to make extra sure, don't use one of the canned flag reasons like "low quality"; click the "other" box and type an explanation.