Inconsistent enforcement of the company's rules, which is the core of the letter is very much working conditions, and his behavior very clearly shows that he is not bound by those rules.
That's not even close to being considered protected activity.
Given you've spammed this misinformation all over this thread, despite being corrected on this point repeatedly, I'm not sure you're acting in good faith.
I've been corrected by folks going, "nuh uh". A discussion about retention, recruitment, enforcement of workplace policies, and airing of collective grievances is within bounds for protected. Provided it isn't deliberately offensive, an individual grievance, or knowingly false.
