Hmmn, I can see why after the interview you felt you were in with a fair chance, but after the interviewer's last comment the day after, well, that would sure have been a warning sign to me!
I still don't think the company has done anything underhand - it seems nterviewer doesn't like being the bearer of bad news. There's a lot of spineless managers about (still!) you know.
Since it was internal, you could ask your manager for feedback on your interview performance - ie where you went wrong, what others did that was better. Although you may feel it, don't be accusing/resentful in any way - you are just looking for constructive criticism, here to learn, yada yada. You might get a better understanding of what's really going on (if there is something) - though if your manager is as evasive as he seems, you may have to perserver v diplomatically...have different approaches - eg specific and direct questions prepared...or tell him where you think you went wrong, and ask for feedback...
PS was your manager the interviewer??