Keep in mind that it's written as "maximum (90 fps)" not "maximum 90 fps" or "90 fps", the () have meaning too but it's currently unclear.
It's strange that they set all the others as a clear limit but not for this one.
So for me I understand it as: "maximum your hardware can do, but we can't guarantee/force higher than 90 fps. good for you if you do."

But until they clarify or people actually test it once it's live. my guess is as good as any.