The phrase "taken short" and the phrase "taken up short" refer to a situation of surprise. When one is "taken short", one has been surprised and one's expectations have been contradicted, confounded, or otherwise proven false.
Often, these phrases are used to describe a situation where a person was prepared to speak, but due to surprise has to stop the act before fully starting. There is some literal meaning to the phrase, which we can imagine, however, the "taken short" can be seen also as a figurative phrase drawn from common speech.
Phrases like this qualify as colloquialisms, figures of speech that often have figurative meaning and come from common speech.
Colloquialisms appear often in literature since they provide a sense of actual conversation and use the pronunciation, grammar, and vocabulary of everyday speech.