Are liquid and dry measuring cups the same thing?

While the volume of liquid and dry measuring cups is the same, there are a couple of reasons these measures are not interchangeable.

Dry measuring cups are designed for dry ingredients, such as flour and sugar. Unless a recipe specifies a different method, dry ingredients should be measured by spooning them into the appropriate cup and swept level with a straightedge.

Liquid measuring cups are clear so that as the liquid is added, you can easily check them at eye level for accuracy. Liquid measures are designed so that the liquid never comes right to the top, making it easier to get an accurate measure without spilling. Liquids should be measured while the cup is sitting on a flat surface, not when you're holding the cup in the air.

If you tried to measure dry ingredients in a liquid cup, it would be impossible to be accurate because you wouldn't be able to level them. And when a dry measuring cup is filled to the top with a liquid, surface tension in the liquid allows the cup to be overfilled slightly -- the liquid bulges a bit above the top. This results in inaccurate measurements.