Are we talking about this edit  That looks like vandalism to me I have no idea who Mr Pena is but the IP modified someone elses comments and added something that looks like irrelevant nonsense To answer your question I doubt theres a written rule anywhere about removing obviously incorrect warnings but it falls into the category of things that are obviously a good idea  If someone is a good faith user we dont want to drive them away by falsely accusing them of vandalism  But in this case I would not suggest removing the warning  you should only remove the warning or replace it with a personal message if the edit was obviously not vandalism