“Military grade” means that it went through one extra round of inspection before it was sent out as far as I’m aware. This round of inspection is basically just putting it through certain weather conditions to simulate “will this survive a deployment”
Okay I just double checked and you’re totally right. When I was in the military someone had told me there was actually regulations around “military grade” and they were just different from milspec. Technically military grade is supposed to refer to milspec but in the private world they don’t check if it’s actually true or not