Yes, it was just a sudden transition for me because the last time I read a Batman raising a Robin story, it was Bruce and Dick in the silver age, or Batman 66. Then in between those years, I heard all about Batman getting more and more dark and broody, so I'm a bit sensitive when I detect that portrayal.
Now, when this was first revealed...
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...the implication was that Damian can't hold his murderous tendency, because he ran away with Nobody, but then it's revealed later that it was just a ploy. So the conclusion is he can control himself, but he still needs to let out that frustration, and he did it through his art.