I don't even play anymore and I still find it incredibly hard to believe something like AV dying can go that unnoticed. As what Aurik said, no one is not going to notice a boatload of people in Sea for 8 hours <_<
That's like going outside, and asking what's the location of the fucking sky. -.-;;
It's also very possible to photoshop it and whatnot, if you know basics it'll look pretty close to those who don't bother to inspect really carefully. However, those who're more adept in the program (ie. Wafik), should be able to make it look like a genuine article, regardless of how fraudulent the image stands.
100 people in DA doesn't mean there's over dozens of parties fighting for Darters and the one malboro for exp >_> Then again, of those 100, maybe 6 could actually exp off them from being able to see them
Edit: About keeping it quiet. If we assume the integrity of the presented material is 100% Accurate, and that AV *did* perish to the aforementioned Linkshell (edited b/c I said Guild@first lol <_<), it is possible to occur. Not everyone likes to be in the limelight, more often than not it's sometimes the better factor into play.
If you start boasting about it, two major things can happen: 1) no one believes you b/c you keep bragging, or 2) everyone and their fucking mother will be asking said LS how it was done, etc. etc. which becomes increasingly annoying overtime.
I guess you can consider AV dying similar to someone unlocking/acquiring Ashbringer in WoW - for those unfamiliar, Ashbringer is the third Legendary weapon, however, no one fking knows how to get the blasted sword. One thing or the other, it's going to be something incredibly fucking hard to go unnoticed outside of the LS/Guild (though not impossible).