Not sure if this is just a mistake by the dev, or Mia is being cagey.
I feel like MC should really be telling everyone about
Lilith being involved in his "accident", as well as her being abducted, and both of them being injected with something. Even if he may be remembering wrong, it's still a huge possible lead. Also, considering all the "concussion side effects" that are much more severe and long-lasting than they should be, it seems like there is zero good reason for him not to tell everything to Naomi and/or the doctor. They might be able to run more tests, and find whatever was done to him in the alley.
If MC tells enough people that Lilith was involved in his "accident", it'd be much harder for her to avoid confronting the truth of what happened to her. Any way you slice it, it makes zero sense for MC to be so secretive about his "accident". Considering it was a deliberate attack, and what MC overheard about their plans for Lilith, at the very least he should be telling every female he knows, so they can be aware of the potential danger.
The end result is that MC being so secretive makes no sense. Not a single person in that situation would behave that way, so it makes his character less believable, and is just poor writing. Other than that, though, love the game.