My dude, 939 doesn't use echolocation. Additionally, that's not how echolocation works, nor how 939 would perceive and process the sounds waves it was receiving. If we were to use your logic of, "the sound would have bounced off the room", 939 would believe that the entire room was shooting at it, because to it the sound waves would be originating from the walls, because it wouldn't be able to track a sound wave off a material that it bounced from. Echolocation works because a bat is the originating source of the sound and knows its own location relative to the sounds it's receiving.
I'm going to leave you two youtube videos to watch that discuss how bats use echolocation, specifically the fact that they use multiple, continuing sounds of various frequencies to track moving objects, as well as how sound behaves in a room for your educational enrichment.
https://www.youtube.com/watch?v=JPYt10zrclQ - How Sound Works in Rooms
https://www.youtube.com/watch?v=laeE4icRYp4 - Echolocation