"The Trash" just sort of stands as a contrast to "The Best", wouldn't you say?
If The Trash Can is an exaggeration, so is The Best. There are at least a few levels in The Best that the word doesn't really fit for, and I think the same is true for The Trash Can. One arguable reason is that they fit more between the categories without it really being worth making another category for them, but really it's just down to opinion. For example, in that one thread referenced a guy got points off for having enemies sequestered into areas where they couldn't reach the player, I wouldn't have made that same judgement since to me it doesn't hinder or improve the gameplay.
At best you can take it to mean that we're just a little more pretentious here, and take feedback with a grain of salt on occasion. I'm sure there's some art or music out there that you would personally think is garbage, and that's okay. However if you really don't want your level in the trash can you can edit and resubmit it while taking the feedback into consideration as well, if I'm correct.