I think he was allowed to remain calm during his time in Marley because he was allowed to have a more "neutral" look at the overall situation: no one around him knew who he was, so he had the chance to fully immerse himself and experience the world from "beyond the ocean" the same RBA did back when they infiltrated Paradis. Nothing had really "started" yet, although he had resolved himself to go through with his plan no matter what.
I think that's also the reason why he had no issues having a mostly honest and open talk with Falco regarding his own philosophy, and his reluctance to go home and how "facing his family" had become too difficult (which was brought up again a chapter later when his grandpa urged him to go back to his family before it was too late and regrets consumed him). Whatever reasons Eren had for not wanting to go back, Sasha's death further cemented the fact that from that point onwards he'd reached the point of no return and couldn't allow himself to fail. That's a lot of extra pressure and it would make sense for him to be very tense or on the edge after coming back to Paradis.
As for the Liberio raid itself, I think his complete calm resulted from the fact that he was personally/emotionally detached from his actions: the Marley military leaders he targeted, the civilians who became collateral damage, the enemy he had to beat (WHT) were only just that.
That doesn't mean Eren's stopped thinking since his return, though: he's still showcasing good judgement and perceptiveness, but all the negative emotions he didn't have to concern himself with in Marley and that have been bubbling under the surface since 106 are now in full display (partly thanks to Reiner's surprise attack which fucked up his plans and caused the situation to escape his control). But the main difference between this Eren and the pre-TS one aside from being a lot angrier is that he can now effectively weaponize those emotions rather getting overwhelmed by them.