Pasta mishap

Last night I went to make my pressure cooker mac n cheese. Only this time I didnt want to use the plain elbow mac. In my store they dont have whole wheat elbow mac. So I bought whole wheat rotini. Normally cooking whole wheat pasta its just in a pot of water. This time was a bit different. The recipe calls for 3 cups of liquid to 2.5 cups of uncooked pasta. With the whole wheat pasta though, there was quite a bit of liquid left so the mac n cheese was a bit runny. not creamy like usual. The only difference was the whole wheat. So Im curious as to why it did that, and if next time I just need to reduce the liquid by 1 cup? or more or less?