If you are allowed resident status after 30 days, is there any way they would know exactly what date you moved into the state? I can certainly understand the 30 day wait to prevent someone from coming in, using a friends address, claiming they were moving there, just to circumvent the residency requirement and get a cheaper license for a day or a week.
But your circumstance is rather unique and military are obviously granted some leeway on licensing requirements.
Your decision was probably the most ethical of the three choices, but I don't see anything wrong with claiming residency status.