Michael Coles had an interesting post about a job interview a friend went on. The person answered questions correctly, but the interviewer told him he (or she) was wrong.
It's a good situation to think about and it's probably one I'll editorialize about at some point. And it's something that's happened to me in the past.
I've had this happen in a few places. Once I was being grilled by a panel of 3 DBAs at a company that was looking to add another. It was a Internet-age company, but one that was fairly large and well-known. If I told you the name, you'd know it, but I don't want to point fingers. In any case, they took turns asking questions they'd written down and one even had a book with him, not sure which one, and they asked me all types of questions for an hour or more. There was a point where I answered something and they mentioned that I was wrong. I told him I didn't think so, explained in more detail what I thought and we decided to look it up.
I was right, not that I always am, but in this case I was and the guy took it well. At least he must have because I was offered the job.
In another case I had someone give me a test, tell me that I missed a couple items and I politely asked to know which ones. They person wasn't really thrilled with debating his test, but I had asked somewhat light-heartedly, so he did, we debated it and agreed to disagree.
I think it's ok to tell someone that you think they're wrong. You have to remember the interivew is a chance for you to interview them as much as they interview you. You should ask questions and even be willing to debate things with them. If they dismiss you, do you really want to work there? You might need the job, so I can completely understand someone holding their toungue about something like this, but I encourage you to stand up for something if you believe in it. Be polite, civil, but firm. It's an art, and practice arguing with someone you know, asking them if you're crossing the line and getting belligerent.
I'm sure there's things that I've told people or believed that are wrong. Maybe I've even asked someone in an interview. However the thing that I often find is that someone who thinks they are always right, or won't let you argue a point, is probably not someone you want to work with.
It's also very likely in a DBA interview that you know more than they do. It's rare that I find smart DBAs interiewing for the position. Often it's managers or developers that think they know more than they do.