Clamshell containers come in different sizes, and are made from different materials. You can buy large or small clamshell containers of berries (strawberries and blueberries for example). Some restaurants offer their to go food in clamshell containers made of card stock or styrofoam.
According to Google images, yes it’s a clamshell. Most people here refer to them as a “container of” <whatever>. For most berries, we have a small (pint) and a large size. Both are considered clamshells