I don't trust for one second when Microsoft says that they've "confirmed" that the achievements were illegally modified.
And i don't trust it for the same reason i don't trust Valve's Anti-Cheat bans and Valve's "our anti-cheat is flawless" attitude either. They are asking players to implicitly trust their anti-cheat software (even Microsoft rely on software readings to "confirm" their stuff), and i honestly don't think they deserve that trust.
Not ruling out that the guy cheated, but i see it as unlikely.
And i don't trust it for the same reason i don't trust Valve's Anti-Cheat bans and Valve's "our anti-cheat is flawless" attitude either. They are asking players to implicitly trust their anti-cheat software (even Microsoft rely on software readings to "confirm" their stuff), and i honestly don't think they deserve that trust.
Not ruling out that the guy cheated, but i see it as unlikely.