Just a thing I want to see, what was the first achievement you got in Halo: Reach? For me it was, strangely, 'Be My Wingman'. Honestly I don't remember playing Invasion the day Reach came out, but hey, I got it that day.
Keep it Clean Killed 7 Moa during the 2nd mission of the Campaign. I didn't even know this was an achievement so when it popped up, I deemed myself the Ostrich Assassin. And I'm 99% sure that when people saw herds of ostriches (or moa) charging at them in their first experience in the campaign, they felt compelled to shoot them.
Doctor, Doctor I think I did a quick custom Firefight on Glacier to see what it was all about. Then I went to Campaign on Legendary.
Knife to a gunfight. Strange… Also the day I got reach i also got the start of something. Wow I must be a matchmaking *****.
Highly doubtful, since you'll get other achievements by accident before you even get an opportunity to attempt that achievement.