Most tell me that any small pumpkins is by default a sugar/pie pumpkins. However, I'm not fully convinced of this.
I am not convinced either
Isn't the sugar/pie pumpkin a separate species of pumpkin?
Yes it is. There are many different varieties of pumpkins.
A sugar/pie pumpkin is often referred to as a spookie and/or spooktacular pumpkin. These normally only grow to 3-5 lbs. The flesh is bright orange, meatier than carving kins, and much less fibreous.
I don't know how to tell, other than knowing they are smaller, without cutting into them. You just got to rely on the store or grower to know I guess