That's my reading too, though I remember someone who wrote a MySQL API layer that was not libmysql was accused of violating the GPL. Amusingly, MySQL is now an Oracle product (though I'm not sure it was at the time).

It had been MySQL's standard MO for a while. Their point of view was you either had to completely open source your product, or you had to pay them lots of money. Using it in an in-house webapp, or as you mentioned, reverse engineering the API, would get them knocking on your door threatening to sue you.

Which is, incidentally, not too far from how GNU/Linux came to be - a free OS with the same interface as a nonfree[1] one.

[1] AT&T was legally required to provide the source code of its OS 'for free', I'm not sure if the terms actually qualify as 'free-as-in-freedom', hence the impetus to create an alternative implementation.