I don't think for self-validation it matters much if someone is a complete stranger or not, it's more about where in the perceived social hierarchy that person

I don't think for self-validation it matters much if someone is a complete stranger or not, it's more about where in the perceived social hierarchy that person sits. Attention from someone who you feel is "higher" in the social tree is a positive, ego boosting signal, and we're wired to react to that. That's the core mechanics behind animal groups organization, and while human society tolerates individualism to much larger extent than other animals, still we're hard-coded to strive for it. I think very few people have such amount of healthy ego that their self-esteem is completely independent from their environments social signals - and it's not necessarily a healthy sign, as it might be also a consequence of some personality disorders.