Somebody has already posted this like 2 years ago but I literally just made an account here to explain something you might like reading. I've just come back from a search to find this bottle online because I actually received one back when it was released when I was 6 (it was released in 2007, my birthday is in december so I must've been around 6). I don't really follow lego at all anymore but it holds a close place in my heart and it gave me huge nostalgia when I remembered the bottle an I figured I'd try to find it and also explain this thing and how ridiculous it seems.
I got it free with 8917 "Kalmah" one of the Barraki warlords I've just had to do some research on. I recall it being with them because of the little jelly-like things that you could fire with the model's crossbow appendage (as well as how I've just seen the name + the packaging). I loved this set but even better, when I got it the lady who worked in the lego store gave me this. It was a free bottle which you got with the model, who'd of thought? It was likely a limited-edition product that was given away for free with the newly released bionicle set or something. I initially thought it may have been a free gift when you spent a certain amount on bionicle sets but it matches the boxing/slogan/theme of Kalmah anyways so it must be a limited edition thing for Kalmah's set.
And now as I recall, we did have several of the Barraki warlords (Kalmah, Ehlek, Pridak and Takadox), which we bought to take on holiday with my brother, we also bought 8893 "Lava Chamber Gate", which was a bionicle playset of minifigures. Pretty fun stuff