It’s highly unusual for the troops to disarm for SECDEF.
When Clinton was still in office it was generally required to disarm. The USSS had done a risk assessment and concluded that it was a highly likely probability that a soldier would make an attempt on him.
Not so strange. I had an active duty marine who didn’t grow up with firearms ask about it being crazy that his roommate keeps a loaded gun in the house. His whole experience is only being given ammo when he needs it so no one has a negligent discharge.