Eh, he didn't really act out of character here. The Bat Family is splintered, his Dad is more or less dead, his girlfriend is M.I.A. and may ALSO be dead, the JL has had its ass handed to it, the heavy hitters have been neutralized to non threat if not outright killed.... him going full Assassin and ambush tactics with his mom just makes sense. And considering Batman's influence on him, when he did to try to redeem his Dad even AFTER some seriously psychologically scarring comments that in some ways are very true... he seemed like the same kid to me from Son of Batman. A bit more mature, and jaded due to some HUGELY life altering events, but still recognizable.