The mod will only highlight choices that matter and will affect whether you choose to pursue a relationship or not. Personality choices (knight/joker/smooth) are purely for flavour, so there's no need to highlight the correct one; the only correct choice here is the one you think fits your MC better.
For what it's worth, looking at the script files, there are two options for that scene. One is a variant for if you're trying to get with Harlow and the other is if you're not. The only flags associated with the choices seem to involve whether you want to keep things going (relationship-wise) with Erika.
It's kind of an odd way to phrase it because it seems to imply that it's a choice between them, but there's no Harlow flags involved in the script, so I'm thinking it was possibly meant to reflect that the MC is still in a monogamous mindset. There's been very little hinting at him wanting to start a harem outside of a few loaded answers to dialogue unrelated to relationships, and him fucking around a bit with most of the girls. Which, hey, none of these people are committed yet, so whatever.
Take all this with a grain of salt, obviously, because I don't know where the story's headed and I'm going by the title/desc/tags this game has re: future harem stuff.
I should probably mention I didn't get time to finish this update, and only came here to double-check that this was still a harem game when I came up on that choice, lol.
. Acting all rational with Erika was sometimes kinda funny too.
