I had never noticed "chumbait" either, though I used chum in fishing once--in water clear enough that I could see the fish eat the chum and turn up their noses at the bait--and I had never seen that use of "that's," which I can't imagine getting used to, much less using.
The Google-equivalent on The Good Wife / Good Fight was called Chumhum, for whatever that's worth.
Using "that's" for "whose" feels like hypercorrection to me, dunno.
I had never noticed "chumbait" either, though I used chum in fishing once--in water clear enough that I could see the fish eat the chum and turn up their noses at the bait--and I had never seen that use of "that's," which I can't imagine getting used to, much less using.
I meant "chumbox" not "chumbait." My fingers did that.
An easy mistake to make!