The planet in that episode wouldn't qualify for Federation membership, since they clearly have no one-world government.
Unless there's no hope of Discovery (or at least the crew) ever making it back to 2257, this question is still open.
What's the latest on that, BTW? Have the showrunners abandoned all hope of a return to the 23rd century? Will the 3rd season involve any attempts to do so?
Unless that Colt was an alien who just happened to have a name that (when translated into English) sounds like Colt. The real, human one could also be on the ship, elsewhere.
Which seems more likely, anyway. In TOS, Colt was not a bridge officer. She was just a yeoman.