What about Mathis, though? His 40.5% is higher than any of the challenging Democratic House candidate in Alabama that year.
Some conservatives who hated Roby didn't know about the write in campaign, and so voted D in disgust.
I find it really difficult to imagine Trumpists who are disgusted by a GOP candidate being "Never Trump" would vote for a Democrat out of pure spite, as opposed to just staying home.
I mean some might do that, but staying home seems like both an easier and more coherent thing to do for those who didn't know about the write-in campaign