Special Delivery&ODST Ach. Unlocked, but how?

So I was playing Extraction on Shatter, just defending one of the extraction sites, when suddenly after a normal melee kill, a pop up shows up: Achievements unlocked: 2 for *** G. The achievements were Special Delivery & ODST. The first one requires you to beat down an opponent as you land from a man cannon. The latter requires you to kill someone while airborne from a man cannon.

The weird part is, I didn’t use any man cannon or something, cause is was just inside the base. Just a sudden achievement unlock with for no reason. Kinda weird… Thought this might be something 343 needs to know…?

Its glitched I think. Same thing happened to me for the ODST one, but all I did was Highjack a Mantis and beat it to death.

Friend of mine got/did the same thing, a few hours later he said it went away, so I have no clue if the glitches are permanent or not

The strange thing is that it says i’ve unlocked the achievements on xbox.com, but Halo Waypoint says i haven’t O.o