It depends on what skills are necessary to succeed at test X and Y. While the subject matter or details thereof might differ, it's possible that things like "knowing how to learn to the test (i.e. cramming)" or "reading between the lines of what the teacher/professor says is relevant" belongs to these skills. And these can absolutely be transferred between test X and Y.

So the question is, how much do these tests actually test skills in the subject matter and how much do they test "meta skills"?

The research shows that the tests are predictive almost precisely to the extent they test “meta skills”. We can even measure how much individual questions test meta skills vs specific skills. You can learn about this by searching for the terms “factor analysis” and “g-loading”.