Multiple discussions concerning comments on review audits have been raised on MSO, I believe this particular one as well but I can't seem to locate it. Basically, it's not a huge concern.
As slhck pointed out in comments, the fact that you actually read the post means we got the action that we were hoping for out of you. These are designed primarily to catch people that are just going through the motions to get a badge, while helping folks to hone their moderation and review skills.
If this had been a real world scenario where the post was still live on the site and you just happened upon it while looking at a question - you would have taken one of the correct courses of action by commenting or editing in an effort to improve the post. That's all the audit was trying to confirm - though it was programmed to expect you to recommend deletion because that's the workflow that was presented. Your call on this one was equally valid.
Those that this would catch just blindly take the path of least resistance in order to get to the next item and advance their badge progress, and they would have failed this audit. Additionally, someone that didn't feel any action was needed with this post and thought it looked good would have (hopefully) learned something.
Audits aren't perfect, but they don't really need to be in order to be effective. Someone paying attention would quickly be able to figure out the post had been deleted anyway, and those aren't the folks we need to be worrying about.