Given the slight time difference, is it just possible that they might be busy enough as to need a second person at the desk? Trying to Think Well of Others here...
Though even then, they should've said something to you, like, "Oh, we're going to be getting some backup for you." Or something.
EDIT: OK, so many ninja posts. I dunno. I'd be tempted to call him out and say, "So were you going to tell me that you're trying to hire someone new for my job?" and watch him turn seven different shades of purple. But then, I have no qualms about making another person feel awkward if I feel they deserve it.
Disclaimer: I am in no way advocating or condoning such behavior. I am merely pointing out a possibility that the bosses should have considered when they started playing shenanigans. Your mileage may vary, void where prohibited, this product was packaged in a facility that handles nuts.