Tell the testing people you are looking for material that will hold water, let them know you are working on a pond and you want it to hold water.
There are other test they offer that will give you that information.
With the PI the higher the number the more clay you have. In our country a 15 is good for a house pad 30 is good for a pond.
If you have paid for the soil to be tested---tell the testing company what you want and what you are doing----ask them to interpret the numbers for you.