Huyang says he helped Kanan Jarrus to make his lightsaber in the Jedi temple. Kanan was known as Caleb Dume at that time, and Huyang refers to him as such; he may have learned through the Jedi and rebels with whom he later worked, such as Ahsoka and Hera, Dume's new name.
Shortly after the "zombie" stormtroopers break through the door, one of them trips on the stairs.