but he said and i quote:You could also keep in mind that Nomura hasn't confirmed the fight to be canon within the plot. The character is definitely canon because there would be no point but they put him there to show he's to come. It doesn't have to mean Time Travel but it doesn't have to exclude Young MX either.
Edit: And no one can really prove or validate anything. That's why they are theories and speculation of someone we have only seen 8 secs of.
I dont like getting in to complicated crap like that but its the only possibilty, he is MX when he was young.
he seems pretty sure, positive really, that this is the answer