yeh i heard that one myself, talk about Chinese whispers. Its simply slander probably created by some p1ssed off vegetarians.
You get them at the wee kiosks, you know the ones, with a thin slice of meat and mostly cabbage ;)
I remember one of those badboys when i first visited Poland i was like what the hell is this shite and proceeded to scrape off all the cabbage, kidney beans, sweetcorn and such. Polish burgers in general absolutely suck.
Ironically not so long ago i managed to eat a whole one and quite enjoyed it, thats what 5 years in Poland will do to ya.