This answer used an HTML comment to subvert the "Your answer is too short" error.
Should HTML comments not be counted as part of the length of an answer? (Similar to how spaces aren't counted.)
I don't understand the problem. It was a fitting answer to a fitting question. If it was a legitimate question the answer would have been down-voted into oblivion or simply ignored.
As for the HTML comments, these instances are rare and most answer are longer than one sentence. I see no reason to actually change anything.
If you really want to go through the effort to post a short answer, then fine. I don't think it would be worth the effort to strip out all the possible ways of cheating that system.
One word answers will probably get downvoted anyway. And zero word answers should be flagged as spam, since they are just wasting space.