What's wrong with the interviewer wearing a suit?
There is nothing wrong with wearing a suit, and it may be common in some workplaces/cultures, but in others it can be corollary to a work culture you are not compatible with.
When I last interviewed 15 years or so ago, I wore a jacket and tie (though not a suit) when I interviewed in person. I certainly didn't think it was necessary but I'd have been shocked if anyone had considered it to be a ding.