From what I can gather, the event happened in 2008. At the time gentoo had no official wiki, it was an unofficial wiki that died or went offline for a significant amount of time.

<https://web.archive.org/web/20081023145740/http://www.gentoo...>

And when it came back online in november,

> Gentoo-Wiki recently had it's database lost; this is the rewrite of the site

<https://web.archive.org/web/20081204053828/http://en.gentoo-...>