Yeah, me too and I forgot about the spoiler tags too which is silly of me.
And yeah true. As you said, he may recently (during s24) have decided they don't treat him well and just got angry and said it without meaning it.
But the thing is they gave us no reasoning or meaning so all we can do is speculate resulting back to the idea of lazy writing. From what they told us in the episode, Carl never liked them right since S1(/2?) which is just dumb and simply untrue!
Didn't want to post after Handsome's post cause you know, further spoiling.
I pretty much mirror your thoughts though.
I can see it probably wasn't the writers intention but they still put the dialogue in there during his huge back-story reveal and it's just awful stuff that makes his character completely unlikeable.
And yeah, the NHC can have you write hundreds of words on the most meaningless sign gag. Welcome aboard.