So you found dirty trash in a trash center. What are the odds in that?
I've had over two dozen keyboards from recycling centres by now so I'm more than aware how dirty they are on average. Some keyboards you'll see in a future review were very bad too. This one is the worst I've seen so far though.
Also, you'd be surprised how clean some of the things I get at the recycling centre are. My AEK and Dell AT101 (non-W) were almost immaculate when I got them, for instance.