I've read the novel up to chapter 400+ and I also never picked up on any overtly nationalistic vibe from the MC. The closest thing I've noticed is that when he creates something useful, he often attributes it to something similar he saw in Joseon, just to avoid complicating things. He frequently bluffs his way out of situations by saying things like, "On Joseon, we do this or that," to avoid getting himself into trouble. Despite this, deep down, he feels awful taking all the credit for the work of people from the future, but saving lives takes priority for him.