The article does not mention anywhere that the amount of water on is more than the great lakes system.
Firstly, the water is in the form of hydroxyl and the mineral apartite (article didn't go into more detail). Secondly, TFA states the amount of water is under 5ppm. Yes, parts per million. I can't see how anyone could arrive at the great lakes value unless they took the volume of the moon and took 5ppm of that, which is ridiculous.
Firstly, the moon's not a uniform material. Secondly, to get anywhere close to this amount of water, you'd need to mine and refine the majority of the moon. It's like saying we have 300 quintillion gallons of water on earth while neglecting to mention that 97% of it is salt water and some more of it in the ice caps.
The real takeaway from the article is that the previously estimated amount of water was 1 ppb and now it's around 5 ppm.