This is correct. Every serious criminal won't use a VPN or other obvious crypto, because this paints a big target on your back signalling you want to hide something. A serious adversary will, as you say, use a pre-arranged innocent vocabulary that is virtually impossible to detect, or just communicate face-to-face or via written notes delivered by a messenger.
Oh and by the way, remember to buy lettuce today ;) ;)
Oh and by the way, remember to buy lettuce today ;) ;)