Fresh pumpkin flesh is about 6g carb per 100g which is definitely lower than potato but without weighing how much pumpkin is in your ladle of soup then there’s no way of knowing how much you’ve eaten, depending how much onion you used that could also have added a few carbs, if it was just a drizzle of coconut cream then the carbs in that would be negligible
Veggies in soups can add up surprisingly quickly - also if it was liquidised it would take less digestion and could have hit your blood stream quicker.
I’ve learned that if I want to make a soup I weigh everything then add up all the carbs and portion it out so I can get how many carbs per portion. Bit of a faff but worth it for a good soup