fishyone,
That does sometimes happen. I had a lawnmower blennie that committed carpet-cide through a gap like you've described. My blennie, though, was trying to escape an ick epidemic I had going on in my tank at the time. My guess is your clown may have chosen carpet surfing to being in your tank.......if the tank is only five days old, I'd suspect it isn't cycled yet and the water quality may have been bad enough to "chase" the clown out. I think you'll find that, as fish become comfortable in a tank with good water parameters, it will be less likely to try to escape.
Sorry for your loss. I wouldn't add any more fish until you've confirmed that the cycle is complete.
Jim