In a custom single player game (1v1), I came across an enemy war galley of the Shang attacking a building of their own. The ship was attacking a house (apparently). The unit was highlighted, as if the thing this vessel was attacking belonged to me. No building nor unit there were receiving any damage. The arrow attack sound was also audible.
The unit being highlighted while shooting an arrow:
Screenshot using No Fog and Reveal Map cheat codes. Arrow is signaled within a red circle:
It was not the dock the thing the ship was attacking, but apparently that house on the right corner (arrows went past beyond the dock, but the screenshot I took made it look like the ship was attacking the former).
It really has some weird bugs… Let’s not forget the scout/lion one, with both units repeatedly attacking the air for some reason.