well iam guessing that being it was a shovel handle that it probably had to much runoff and would have btoke even if was used for shoveling
personally i dont like using kiln dried boards,but thats just me.i do make board bows but try to find a mill that air dries their lumber
it is harder to find that way these days,but after 110 mile drive(one way )i have enough for 5 board bows.
i try for quartersawn lumber myself,but there are other cuts that work well also.
ifn you can post pics of the broked wood and someone is sure to have the reason as to why it failed