Obviously you know your friend better than I do, but he has similar results and backstory as me. Have you guys considered INTP?

It’s not uncommon for INTPs to have high Ni. Mine was second highest just barely below Ti. They also have higher Fi. And Se is dead last for him which would indicate shadow function (thats what someone told me about my last Se as well). My Fe was also bit higher than Si because I answered some questions from a social anxiety POV.

And I feel like INFJs having aux Fe would naturally be good at reading body language and cues. Dominant and auxiliary functions are part of your nature and don’t need to be worked on like the last two functions.

Then again.. I also grew up in an emotionally oppressive home. For all I know you’re right in your theory and I’m an INFJ who leans towards introverted functions too lol anyway, just a thought to consider if you haven’t already.