Honestly this feels more like a deconstruction of the tsundere trope and should be taken as a chance for the MC to point out to the sister how her constantly demeaning him to others had nearly fatal consequences for him. In a world like this where she's a famous adventurer, she supposedly was constantly going around and calling him useless and trash, and should have known that her words carry a lot of weight among people that look up to her. And then not even a minute after reuniting, she calls him her "hopeless brother", in the same instant doing that "But it's not like I was worried about you or anything!" schtick. I forget what happens from this point forward regarding the sister, but I do desperately hope she learns that she should not say such disparaging comments to others, since her words due carry weight due to her fame.
Regarding the MC, I dunno if he'll forgive her, but I don't think it's that wrong that he shut her down at this point. She basically has ambushed him, the mental stress and anger he likely feels towards her has to be immense, and it's not like he said "Never approach me again." or such, so she'll presumably have the option to arrange a reconciliation with him, but it'll have to be on his terms, not hers.