I didn't earn the "edit community wiki" privilege on Stack Overflow, but it shows in the recent achievements list.
I'm pretty sure this is the same case as @SebastianSimon found on Meta Stack Overflow. Apparently, this question hasn't been asked on Meta Stack Exchange yet (or my duplicate finding skills aren't working before the first coffee of the day).
Your reputation tab shows no net changes for the day:
Following the template from @Oded's answer there:
Why bother with it if there were no rep changes?
Well, that's not true - there were rep changes, but the sum total (net) of them was zero.
That means there were some votes happening that got reversed (most likely an accept, taking you over 100, followed by an un-accept).
Now, you were briefly at 100, so you got the privilege - and a notification was sent and received.
We don't retract notifications, so you saw that, even though that by the time you got it, you lost the privilege :/