Remember it's not the size of the boat, it's the motion of the ocean... oh wait that's something else....
Sometimes (mostly in Cozumel) we broadly classify a cattle boat by the size of the boat and not necessary the experience. Pretty much anything bigger than a panga or six pack boat becomes blanketed as a 'cattle boat'. But obviously that's a really broad stroke, especially outside of Cozumel where large boats are preferred due to the comfort they afford in conditions that aren't the glass like conditions we are used to diving the sheltered dive sites of cozumel. Outside cozumel you'll typically be on larger boats and have 10-25 divers on board, but the diving and divers could easily be much different than cozumel, you could easily find yourself in the water without a dive master, where the boat is only a ride to the dive site and nothing more, so the cattle boat operation I'm more careful to classify based on the experience not the boat, I'd consider it 'cattle boat' when you got tons of inexperienced divers being herded by the dive op as quickly as they can in and out of the water, where the operators focus on profits instead of diving is very transparent. Snorkelers on a dive boat is not always, but sometimes a good indicator you're on a cattle boat.