Accidentally Unlocked Thanksgiving Activity Achievement?

[NekoMichi]

I seem to have accidentally unlocked the special Thanksgiving 5K achievement and sticker in the Activity app despite the fact that it's not supposed to be available on my system.

My iPhone is set to the UK region and has never been set to the USA region before, the Thanksgiving achievement isn't supposed to be available to me. Similarly, I haven't done a workout exceeding 5K on Thanksgiving. On the day, I didn't receive any notifications about the achievement and even after the day, the achievement did not appear in the achievements list. However yesterday I had to change my time zone setting because I flew from Europe to Asia (region format setting was not changed) and while checking the achievements list it shows that the Thanksgiving 5K achievement was unlocked. (please see attachment)

Is this some kind of glitch? I haven't received any notifications through the Activity app, and wouldn't have noticed this if I hadn't manually checked the Activity app. The December Perfect Month achievement also seems to have been unlocked even though December isn't over yet.

Info:
iPhone 7 (iOS 10.1.1, non-jailbroken)
Apple Watch (First generation, watchOS 3.1.1)

 

[Just_Me_D]

Not sure. Your post is the first I've heard of it.