Does the Frying Pan knockback enemies
Two things.
All damage causes knockback, even DoTs like burning and bleed (just try and keep your scope steady as an immolated Sniper!).
Crits get a significant amount of bonus knockback.
This means, if you crit, you can knock someone back a goodly distance.
If you noticed it happening on non-crits, or on every swing, then it's quite likely it was related to the server you were on, because the Frying Pan is simply a reskin of the stock melee weapons of the class that is using it. (I.e., Scout's Fryingpan is faster but deals less damage)