I'm going out on a limb here with speculation: wall paint, tesserae and other signs of high status finishes to interior, and things like a hypocaust and food preparation spaces which don't meet the formalisms of a military facility. That said, I read of military owned staging posts with pretty high investment features like baths. 5 star roadside hotels for senior staffers and government officials on the move. So dual use, or military but fancy is possible. Also not an archaeologist