I believe you can face any other person that is doing a mission. I've heard people say they've come up against region two characters while doing missions in region one. Besides, the characters are not what decides the battle, it's the strategy that you use. If your strategy is good enough, you should be able to beat these characters.
its cuz theres this 'star' system now, and they could use that as a way to know how far you are in the story, thus facing ppl somewhat near you.
and i didnt faced anyone with the new chars yet, hope it doesnt occurs soon...

Thank you ppl who helped me to hatch my poke eggs ^^
And her you can find my other eggs, fell free to hug them if you want:
Here
(ps.:you need to click the buttom under the egg to hold it, and give a berry to the poke to feed it)