OK, I see we need some laws read into this situation. First and foremost, if he was military and discharging his duties, he is allowed to open carry anywhere in Texas. 46.15(b)(1) makes 46.02 non-applicable to the military in the discharge of their duties.
Second, only the military can say what the discharge of their duties are. While dropping a child off at school may not sound like official duties, he is in the discharge of his duties if he has regulations requiring him to be armed at all times.
Third, there are so many exceptions to the Posse Comitatus Act that it is almost null. Active duty military can assist local police in many cases, such as drug cases, weapons cases, and border patrol. Two examples of this from Texas history are the military helping the ATF/FBI at the Branch Davidians compound in Waco (one of the complaints was that the ATF lied to Ann Richards by claiming drugs were involved to get he military equipment and training) and the shooting of Ezequiel Hernandez by marines on border patrol.
And given all of that, my money would be he was a poser. I am not involved in the military and have not been since 1983, but I know of no regulation requiring anyone to be armed 24 hours. I know general officers used to be authorized that privilege, but even they were not required to be. And, as many others have pointed out, most of the special operations soldiers do not tell anyone they are in special operations. Those that do will usually claim their branch, not spec ops (except for a very few whose branch is still classified - like Delta Force was when it was first started). I strongly agree that the police should be called if he shows up again.
There is an Armed Force Police unit in San Antonio that can tell you if he is active duty and where he is stationed. They would take a report on this incident and refer it to the appropriate unit if he is in violation. The MP's at Ft. Hood would probably also due this. I recommend the current incident be reported to the military to prevent a case of
stolen valor.