The phrase "low calorie nut" is a misnomer since all nuts are high calorie. That said, cashews do have less calories relative to most other nuts, especially Brazil and macadamia. But do cashews contain antioxidants in greater amounts? No, they have an ORAC value comparable to those two and versus most other common nuts, cashews have very little antioxidant content. For example, peanuts have 50% more, almonds 120%, pistachios 280%, walnuts 575%, and pecans a whopping 800% more antioxidants. So while you may be consuming 10 or 20% fewer calories with cashews, you're losing out on a lot of nutrition with them.
Because they are a relatively cheap nut, you are seeing them used more in processed products such as vegan cheeses and cashew milk (instead of almond or flax milk). This is somewhat unfortunate since they offer less nutrition and are an under-respected allergen. The percent of the U.S. population which has an allergy to cashews and other tree nuts is 1.1%. This is almost as high as peanuts, which is 1.4% (and in Canada the order is reverse - tree nut allergens are a higher percentage versus peanuts). This is according to a 2010 study published in the Journal of Allergy and Clinical Immunology (source).
Many are surprised to learn that cashews grow on a tree, Anacardium occidentale, which also produces an edible "apple" known as the cashew fruit.
USDA Database for the Oxygen Radical Absorbance Capacity (ORAC) of Selected Foods, Release 2 - Prepared by Nutrient Data Laboratory, Beltsville Human Nutrition Research Center (BHNRC), Agricultural Research Service (ARS), U.S. Department of Agriculture (USDA) - May 2010