I agree, that one was an incorrect answer that was still counted as correct. The user meant father, while they should type mother.
In the other examples above however, the user means for example kyuushuu, but simply doesn’t type it well. So I’d say that that still counts as correct.
To be 100% sure you’re typing the right word, you can always install the script down below. When something is not precisely correct but Wanikani counts it as correct, the box simply shakes and asks you to try again. Very handy 
I agree with you that these results are pretty strange, but fixing it would be a Sisyphean task.
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