Ice cream has to be at least 10% butterfat and 20% milk solids according to the FDA.

DQ soft serve is 5% butterfat so would not legally qualify as ice cream, though it would qualify as low fat ice cream.

I do believe that most soft serve is a similar fat percentage, and also has much more air per volume than traditional ice cream.

Also, I must say as an ice cream aficionado, I do love me some soft serve and I would never disparage it by calling it “not real ice cream.”