The only option without including bugs I suppose.
I can't find anything about this theramore bug at the minute save for 1 person (?) mentioning a drop on the US forums, I would've expected some more drama around this tiger if it was something as widely spread as a CtA bag.
Using widely spread loosely as there isn't a lot of CtA going around anymore to begin with.
Theres some funny stuff going on with shared achievements. This week I logged onto an old Vanilla character that had the "Sergeant Major" achievement. For whatever reason the date on the achievement changed to the day I logged in, not when I originally had it. However, I also received "Corporal" achievement with an achievement date of 10/14/2008 from a character I logged on 2 minutes later.
I'm guessing this guy logged onto an old Vanilla alt that had the achievement and a similar thing happened. Could be wrong though.
I got my Hydraxian achievement (again) the other day when I killed one elemental in Silithus on an alt. I've been exalted with those guys for years, but since the last patch, something funky is going on.
He has the tiger on another character and the day he did the Theramore scenario was the first day he logged in on that character, so for that character it shows he earned both achievements on that day.