mysql being or not being slow, along with postgresql scaling well, have nothing to do with the story being posted. your comments are being downvoted for being off-topic.
The point of the article is that basic functionality you need to get MySQL to scale well are no longer available as 'open source', but only in the enterprise product. That seems to touch on 'open source' postgres scaling, as well as mysql being slow (well, unless you pay for enterprise it seems).
That is a reference to waiting for queries to finish.
Mysql is slow.