I understand the confusion—you are correct that pH doesn’t exist without the presence of water. However, in this context one can view it as how protonated/deprotonated compounds in the extract may be.
When you pass a mixture (without water) through a powder that exhibits alkalinity when suspended in water we claim that the mixture is becoming more alkaline or higher pH. What should really be stated is that molecules are exhibiting behavior that would be typically seen when they are exhibited to alkaline conditions.
Hope this is clear and helps.