In response to previous questions, there was no name mentioned in the posting, just a comment about seeing a job candidate's teaching demo. Also, this colleague is not on the search committee.
Oh, wait a minute. I thought the offending colleague was on the search committee. S/he was merely an audience member? In that case, I don't see much problem, even if the other two candidates saw it. I'd see an issue if this person was on the search committee, but the opinion of an audience member has no direct bearing on the search.
Sure, it would have been better if s/he hadn't posted the post--but I truly don't think it's a problem that s/he did.