I did not expected it either but also not entirely surprised. I noticed about "otome" style isekai (well this is not but lack of a better word of this subgenre of a person having foreknowledge of a bad future and given a chance to redeem themselves with heavy tendencies of female protag and medieval-fantasy settings)tend to bring up more topics than many others - like MCs who actually have attachments to the old world and its implications on the character.
But it also still really too early to tell. I'm pretty sure this reveal, while unintentional for her, is a step forward to making the prince a true ally. Changing the course from him hating her to wanting to protect her - if this will be more comedy-based, I expect a misunderstanding of him thinking she hates being forced into a marriage far away from home which he will instantly relate and build attachment due to his background. Or she will reveal (or eventually) reveal her true history, creating a similar effect but less comedic and more serious. I could be totally wrong too.
But regardless of my guesses, I'm sure the story direction is for her to not be the villain and become liked similar to Bakarina. The interesting implications that I am wondering is how far this story will explore how much it may change his destiny. Since the point of divergence is so early in there life, the possible butterflies can be huge. And far, unlike other similar stories, there no "constants" (to borrow a term from Bioshock) established so far like some future high school everyone will go. Without no such constants with such influential conditions from such hardships, it can really shift how he would grow up - his personality, his performance in the military, his future of becoming the hero, and a ton of other stuff can all be changed.