The commander had left the cell door open. The princess made it clear during their last briefing that the alien was not a prisoner, but she had also made it clear that it was rather fighty, and not overly fond of strange ponies. Auburn wasn’t on duty when the princess sent a young doctor down to try and stitch the human’s lacerated forelegs. But apparently she ended up fleeing the cell less than a minute later. Nopony ever found out why.