Bernardelli 22 What Is The Definition Of A Small Frame Handgun?

What is the definition of a small frame handgun? - bernardelli 22

I was at my local shooting range "small scale", said handguns are not allowed. Apparently, these include on my Kel-Tec 9mm. Sig Sauer Bernardelli .380 ACP and .22 LR. I can accurately hit the target with the 25 meters. I thought that meant a small scale, like the gun derringer.