A bong without a screen is still a bong and the only reason I can think of for the use of the term "poppers" is the sound the bong makes as the pressure inside the bong becomes so low that the contents of the bowl are sucked into the bong itself.
However I hold by the info I gave as it is correct usage of the term poppers where I live and since I did read the posts above my first comment (which BTW is for the info of others) it would appear that it is also the same as in the US.
Canada does have a rep for being a little odd