Did he put allied lives in danger? Did the truth damage our long term interests
Someone in the Lt Col's chain of command decided the information was classified.
You are unable to answer any of your posed questions including, especially, the two quoted above.
Perhaps the Lt Col's seniors actually do know better then he and thee? Perhaps not, but it was not his or your place to make that judgement. I'm pretty sure it says something like that in the fine print of an enlistment or commissioning oath.
Selective leaking of classified by a military member is not an option I would think.