Yeah, point. The answer did make me angry for that reason. But maybe she was counting it as a win for him because he already got the vaccine and focusing solely on trying to explain the parents' probable POV, which no doubt is that gross given their reaction? The LW did mention his friendly relations with his parents, so that could have given her the idea it was the primary concern...

...very wrongly though, since the actual question was "Did I do the right thing" and the brother's agency is the central issue to that.