Of course I have looked at the schoology page as soon as you posted a message with the link!
But all I see is just a field to enter a percentage for partial grading of the alternate answer.
So I can't imagine how the system can calculate the 50%, 33%, 50% grading for the mix of correct and wrong answers.
That makes no sense to me.
Have you effectively tried this question in Schoology and are the grading conform to these figures for all combinations of correct and wrong answers?