But why was the GOP turnout so low and that of the democrat’s so high?
You’ve answered the question of why this special election was a nailbiter when it should have been a romp. But the above question (actually 2 questions) is a red flag.
Can anyone explain these questions of turnout?
Just an educated guess, but one big factor could be that this special election was held in August (somewhat unusual, I'd say). And it was merely for holding down a House seat for a few months.
Many potential voters in this Ohio district probably didn't even know that there was an election yesterday; others might have been on vacation (August is peak vacation season) and had forgotten to ask for absentee ballots. The same considerations don't hold true as much as for the Democrats, who are better at voter organizing and cheating.