Humus is not just soil, it is a community of living things. Organic matter is a breeding ground for many types of microbes, including bacteria and fungi which break down plant material, and for other microorganisms that help plants roots absorb necessary nutrients.
I agree with your analysis, but I disagree that cagers refers to an entire class of persons, all motor vehicle drivers. To me, and maybe I am not using the right definition, a cager is an @sshole motor vehicle driver.
brute, savage, wildcat, beast, wolf - a cruelly rapacious person. bludgeoner - an assailant who uses a bludgeon. bully, hooligan, roughneck, rowdy, ruffian, yob, yobbo, yobo, tough - a cruel and brutal fellow. harrier, harasser - a persistent attacker; the harassers were not members of the regular army.