How can it be a "connection" if it is only one way?

Adding an npub to my kind 3 just means I'll see that npub's posts in my feed. We've not necessarily made any kind of mutual connection and may have no relationship to one another at all.

All that it means is that I am interested in seeing what that npub has to say.

If it worked by sending some kind of request to connect that had to be approved by the npub I was trying to connect with, then you might be on to something.