In the sherlock holmes shorts story "the red headed league" why does sherlock think he should not explain how he observes things?

What can be inferred from the following sentence in the passage? then he asked me my name. scarcely had i uttered it when he made a gesture of astonishment. a) the sentence implies that the attendant knows the colonel. b) the sentence implies that the colonel is giving up on life. c) the sentence implies that the attendant is going to get fired. d) the sentence implies that the colonel recognizes the attendant's name.