The statement means don't bring a knife instead of a gun. If it's a gunfight, then it will be a full fledged gun fight, so don't split hairs. Yes, you can bring a knife as a back up, but bring a damn gun. Guns with bayonets are fine. But bottom line, if everyone else showed up, out in the open, with guns, you don't bring a solely a knife.
These are the knives you bring to a gun fight.
http://farm2.static.flickr.com/1074/5159419077_20895812b3.jpg
http://www.typo.org/~web/guns/images/mn-with-bayonet.jpg
http://www.ak47bayonets.com/pic/2007-7/00-7-23-07-003.jpg