The quote was written in 1900, published in 1926, but it is in the memoirs of an old soldier who was reminiscing about an event that occurred during the war. I am assuming, from the detail of the memoirs, that he was also referring to records other than his memory, although there are times when his memoirs contradicts the official report he wrote days after the event. But the First Texas Sharpshooters were some real characters, who made a definite impression on the writer.
I agree that it seems unlikely that the writer would refer to smoothbores as rifles.