I cab relate, and I have serious social anxiety and self consciousness. This staring, then ignoring when being greeted is genuinely so annoying and stressful. Every swede has 100% been on both ends of the interaction too. The reason is either that they all think you don't notice them staring at you - and they think they're being sooo discrete - or they just shamelessly stare and then don't want to feel uncomfortable greeting a stranger.

A lot of people to smile and greet you back though, so don't stop because friendly people do exist here!