Cabbage, collards, and kale are all commercial cultivars of wild cabbage, Brassica oleracea. The list of volatile oils in cabbage includes hydrogen sulfide, dimethyl sulfide, and a whole laundry list of similar stinky compounds. Dimethyl sulfide is particularly potent, even at low concentrations, and is known in chemical practice as one of the foulest odors in organic chemistry. And we know hydrogen sulfide as the rotten egg smelling component of lethal sour gas.
But human appreciation of odors is a funny thing. Some odors are always bad. Others are generally considered bad, but that affect can be overcome when the odor is associated with a pleasant nostalgic memory. Many people with happy memories of southern childhoods find the smell of cooking collards to be a happy smell.
But they are strong odors. And I doubt very much that a few pecan shells or a bit of vinegar alters the chemistry. But it's not unlikely that vinegar masks the odors. A bowl of vinegar set out in the kitchen is often recommended to counter all sorts of cooking odors.
"Kitchen duty is awarded only to those of manifest excellence..." - The Master, Dogen