I don't think it's electrolyte leakage. The socket surface below looks shiny, and since there is almost certainly copper and/or nickel present, corrosion damage would have a green/blue tint.
Tin whiskers? Certainly looks like them, and electro tin plate isn't uncommon on older sockets.
I agree, maybe it's not tin whiskers from the socket, but from whatever DIP IC that was in it.