Active-duty military of a foreign nation gets special attention at borders. As you might expect.
When I was in the USAF my unit got invited to participate in a shooting competition in Innsbruck. At the time, Austria was a neutral country (that is: not in NATO or the Warsaw Pact), so we each had a special document from their Foreign Minister giving us permission to enter while in uniform and handle weapons.
This PLA Major knew that his J1 visa would have been held up (best case) or denied (worst-case) so he lied on the application about who he worked for. Customs & Border Protection is actually being low-key about this, because as an officer in a foreign military who lied and entered the country and then worked at a research facility, he could easily have been charged with being a spy.