If a person's urine was constantly pH of 5.5, what would your opinion be??
Urine and salvia pH do not accurately reflect blood pH. And normal urinary pH can be as low as 4.6. Especially if you are testing in the morning when the pH is more acidic. This is why blood pH is a better indicator of true pH.
There are also simple things that can create more acidity in the urine including high protein or lack of water intake. If the urine was abnormally acidic then you would have to look at other possibilities such as uncontrolled diabetes or COPD.