"He eats soup" should be the default translation. To "eat" soup is much more colloquial and common in English, as well as a more accurate translation of the Thai. As of now, "He eats soup" is not even accepted as an answer, which is troubling! I eat soup for lunch almost every day. Have I been... doing it wrong? The only time I might be tempted to "drink" my soup is if it is a thin broth that I sip directly from a mug. If the soup is in a bowl, as usual, and I'm using a spoon, as usual, then I am most definitely "eating" my soup.