Some players certainly adhere to that code, but some don’t, which is also probable. For example, a couple years ago Scott Van Slyke of the Dodgers publicly talked about how his teammates, notably his friend Clayton Kershaw, were fed up with Yasiel Puig.
And I wouldn’t consider it improbable that Pedroia told his teammates NOT to retaliate and escalate the situation, but Barnes did anyway. That’s a story that makes every piece fit, and actually, unlike the popular belief, even explains why Pedroia reacted at all. And that’s just one possibility.
Like I aid, I’m at least open to that and other possibilities, and with an equal amount of proof that anyone has for anything else.
And by the way, your Kimbrel/unicorn scenario is actually NOT possible...