Those tubes were autogated and he probably had daylight filter covers on the objective lenses as well. Both protect against tube damage in high light environments. The means by which each ccomplish this are very different but by limiting the amount of photoelectrons that pass through the photocathode and are converted into electrons. This results in less electrons making into the micro channel plate and that means reduced secondary electron emission. Because of that, less electrons hit the phosphor screen which then results in less electrons being converted back into photoelectrons which are what create the Image viewed through the output screen. So when the the amount of light allowed to enter the tube in high light environments is limited in one form or another, especially when using multiple different forms of light limiting factors in conjuction with each other at the same time, the image isnt able to bloom from over exposure when tube is subjected to very high light levels and damage is less likely to occur.
Im sure that is why he turned them on in a well lit room to show you what they were like.
I cant be positive on this, because you never know what someone else is thinking, but find it hard to imagine that at least a large majority of Navy Seals would turn on a an expensive piece equipment to show someone if they knew it would be damaged or destroyed from doing so. And im sure they would know this as they are highly trained on the propper use of their equipment and have, I would think, at least a good bit of knowledge on the mechanics of such devices that they deploy to help keep them safe in dangerous situations and hostile environments. But like I said thats my thought on that and I could be wrong.