Cosmic fountain is polluting intergalactic space with 50 million suns' worth of material

Why is this described as "pollution" of inter-galactic space? Maybe it would be better termed as "fertilization" if the rest of the article is correct about this material eventually producing another generation of stars. But, do stars form in "intergalactic" space? Or, does the material need to get gravitationally dragged into the originating or some other galaxy before it can become dense enough to make new stars?

And, what about the "filament" structure of this material? If it is really from a huge number of supernovas, I would expect some more cloud like structures, unless maybe the clouds are blocked in almost all directions and the "filaments" are only able to stream out of holes in the other material. What about some other theory for the filament structure, such as magnetic fields around or even between galaxies?