Isn't that exactly what they're doing? Filling it with junk?

my impression is they are sending people actual items that seem new

Are people actually comparing the items that they received to the items in the fraudulent reviews made using their address? It seems unlikely, so I just assumed they weren't.

Seeds?

as mentioned in the article, and from people i actually know IRL, people are receiving electronics or dog toys etc..

Oh yes, people get all kinds of crap in brushing schemes. Currently, though, tons of people are getting seeds, which people suspect is some sort of large-scale brushing mega-project.