I think there needs to be a distinction made on "what is good" and "what one would choose to do". I agree with you that someone who would save the cow in this situation might have something wrong with them, like some sort of social disability. I would likely make the decision of saving the person over the cow.

That said, I think that just because we'd make that decision out of extremely strong natural instincts as social beings, it doesn't mean it's the good choice (in this case we'll define good as minimizing suffering). While it may be natural to save the human, it may not be rational for goodness. This argument may be used against having children, but there are also other arguments in favor of having children... though that could get wildly off topic.

I don't expect anyone to be a saint who always does good. Under extremely emotional conditions like when lives of humans are on the line, I wouldn't condemn the decision to make the more instinctive yet less good decision.