Nah pretty sure it's Tetramorium all right, Just because it hasn't been found doesn't mean it can't exist.
I have encountered a bunch of Tetras (in different colours too) everywhere even have a colony of them but who knows maybe we don't have Tetras
The chances of you discovering/keeping a species that has not been discovered in your area is super super low. I'm not saying it's impossible just saying it's highly unlikely.