Was totally a thing at the time:

The definition of terrorism specifically carves out nation state actors. If Osama Bin Laden were part of the Afghanistan military structure, then he wouldn’t be a terrorist. Instead, he was running his own organization with Afghanistan support, which made him a non-state actor. So drone strikes by a nation state military wouldn’t be terrorism, but would be if it’s done by some rando.

Now, if you want to argue that nation states adopted a definition that conveniently left themselves out, I would agree.