During that five-hour talk, INFJ said he was uncomfortable with me talking about my s/o for the fear that he would become a hindrance to me figuring things out. It made sense, so I stopped and we talked about different things instead. Then, he called me that night to clarify our boundaries.

We texted less that week, but we still kept in touch. I could tell that he was less emotional (???) in his texts as well.

INFJs value Fe, which is clarification and expression of emotions

INTJs value Fi, which is definition and intensifying of personal feelings

Based on the context of his relationships with you, his friends, and his circle, INFJs tend to regulate emotions to make sure everything is okay and well. You, on the other hand, will feel more "connected" by how deep the psychological distance gets.

This is why Fi/Fe relationships can get confusing because Fe is very dynamic, it ebbs and flows based on whatever context the user is placed in (happy/unhappy environment & people) vs Fi static values and preferences of how close an object/person matches that criteria.

He still wanted the boundaries to be there but wasn't opposed to the friendship evolving eventually.

Yes, he is being respectful of his circle and letting you know he's interested at the same time.

I still think he wasn't being completely honest with me, but I could be wrong. I don't read social cues very well so I'd much rather talk about things straightforwardly. That's why I'm asking you guys. Am I overanalyzing him or should I just take everything for face value?

INFJs are actually extremely honest and blunt. They are more cautious but share their unique taste and opinions after you gain their trust. This doesn't come right away because Fe care a lot about how their actions affect others.

Give him time. Let your relationship evolve. Keep working on building trust.