Also there's a lot of variation in how skilled people are at reading emotions. Also a lot of variation in how much attention people pay to small details, and how good a memory they have for them. I've heard anecdotes about Zen masters being able to do things similar to what Holmes did in the story—it's not too far-fetched to think that that level of training combined with one in a million innate ability combined with a decent amount of prior knowledge about a person would give one something like legilimency.