I'm just saying that, reading the rule standing alone, if I were driving a fishing charter vessel and trolling a few hundred yards of line and a floater-thing, I would sure believe -- in good faith -- that I'm fishing under the COLREGs. Is there any written authority that says I'm not?
Remember, to be "Fishing" as a privileged status you must be restricted in your ability to maneuver. What that means is you must be restricted in your ability to maneuver your boat
. Getting a couple lines fouled is a hassle but it doesn't affect (or restrict) your ability to maneuver you boat and thus get out of the way.
Therefore his lines off the back don't restrict steerage, and the fisherman should give way.
(though I agree that racers often feel more privileged than the law allows)
Also, it's a common misconception that just because the guy has a business license that somehow makes him commercial and that the status of being a commercial vessel actually gives him any rights.
I could have a corporation that owns my boat. Who cares? It's not in the colregs that a boat has rights because it's owned by a company instead of an individual. If I want to hang 200ft gill nets off my boat and display the cones, I'm Fishing with a capital "F" regardless of if I have a business (commercial) licence or not.
Any chance that when he was yelling "Hey we're fishing", he actually just meant fishing with a lower case "f" and was telling the racers that they were messing up his day?