Evidently there was a lot of fuss over that answer. Plural, since in fact there are two near identical answers from the same user. The first one was deleted after several flags. If you look at the revision history of the second, undeleted one, you'll see some clues about this.
You are not the only person to flag the second one either. However, you're the only person to have your flag "disputed".
On the surface, in its current form, this is a bad answer -- that doesn't make it not-an-answer. However, in its original form, the repetition to make the minimum character count is obnoxious. Likely that's why Ghanima deleted it.
The user posted the second answer the next day and this did come to Ghanima's attention; he chose to deal with it by leaving a (now deleted) comment for the author. Your flag was raised about 15 minutes after that, and I think it was never dealt with directly by anyone (keep reading as to what happened). Ghanima's comment was never replied to, and the answer was cleaned up by Steve 3 months later following yet another NAA flag.
Of course, this doesn't answer your question directly but:
The thing to do with bad answers is downvote them. Since that user still looks active, at least on other exchanges, s/he would notice that and may delete it eventually -- but I'm not sure what that would mean for the flags.
There's nothing we can do about the flag directly, and deleting the answer (if that would work) for that purpose doesn't seem appropriate.
A disputed flag is not a declined flag and doesn't count "toward flag bans".
I mention this last point because I don't think there's much cause for concern here. I realize this is also your only "disputed" flag and the word implies some sort of resolution may take place, but looking at that Meta.SE post it appears there is not. It also seems to me the classification is one cooked up by the system in certain circumstances, i.e., it is not because a moderator ticked "dispute" (there's no such option). Based on that Meta.SE post and the other one linked at the end, here's what I think happened:
You flagged NAA.
Minutes later, the system flagged VLQ (very low quality). This evaluation is based on length, grammar, etc.
VLQ flags are not necessarily cleared by a moderator; they go into the "Low Quality" review queue and may get cleared there as "Looks OK" by other users. That's what happened here.
Because you had a flag that hadn't been cleared on a post with a cleared VLQ flag, your flags status automagically became disputed.
This maybe clarifies the context of "disputed". In any case, again, I would not worry about it. It is not held against you and you have a high ratio of helpful:declined flags anyway.