No its not at all. I think you're e-statting.
Agreed.
18" is definitely not a 'regular' sized arm and is considered by most very hard to achieve. Put size onto arms takes a very long time they don't respond like other muscles such as the pectorals, lats or quads. BIC3P and FF have those size arms and they are monsters. I've tipped 17" but that was whilst on C-mono so had some water retention.