4 of us stealth chain in the corner, none of us got hit by anything during barrage phase.
I got hit by every attack besides the barrage phase.
Result: I got the achievement but the other 3 people who were in stealth with me the entire time did not.
Conclusion: Achievement obviously bugged as 3 of my friends moved with the same precision as me in the stealth chain, yet I was the only one to get the achievement.
As this event is coming to an end I don’t see anything Anet can do about this so I just wish better QA is done when a challenging achievement is implemented in the future.