I see where you're coming from -- you can't call STRING_SPLIT() directly on the original string to accomplish this, but that's only half of the point of this question. The other half is that there's often a way to accomplish a task which isn't directly supported, simply by changing the way you look at the data or the problem.
Yes, that does require some understanding of data types and how they are formatted. But when you're working with data at production scale, you should have that understanding, or the ability to research it quickly, anyway.
I always try to format my questions so that you can easily run the options in a test instance if you're not sure about the more technical aspects -- I don't consider these questions an exam on anyone's actual skill level, but an opportunity to share and learn.