That was a bad explanation on my part, sorry. They are still open source!
But they diverged from keeping fully aligned with MySQL developments AFAIK so are no longer a fork/distribution as they are forging their own path.
So I was being unclear, the "until a couple of years ago" was referring to divergence rather than a change in license.
So I was being unclear, the "until a couple of years ago" was referring to divergence rather than a change in license.