This study is misleading. If you read page 101 of the study the primary minerals used in the study (calcium, potassium, sodium and magnesium) are all citrates , which are the ACIDIFIED versions of these minerals. They were also using chromium chloride, which is acidic.
Furthermore they also had zinc, copper and selenium in the formula that all form anti-inflammatory, antioxidant enzymes. The reduction of pain could have been from the increase in these enzymes, which have nothing to do with acidity or alkalinity.
And finally they also use a molybdenum source, which helps to rebuild cartilage. This would also reduce the pain and has absolutely nothing to do with acidity or alkalinity.