When I put one avocado into MFP it said 17 carbs and 13 fiber; MFP bothers me a bit because when you punch in a food no matter how specific you are it gives you a list of foods all entered by different members with different name variations and different serving size availability. As to guacamole when I make it at home I use chopped peppers, chopped onions or scallions, sometimes chopped tomatoes, always lemon or lime juice, and usually sour cream. So if your guac was anything like mine it would account for a couple extra carbs, but not that many, the foods in MFP that do NOT have an asterisk next to them are the ones put in by the app everything else is other members all of whom have different recipes for homemade stuff and different ideas about what matters.
Here is a link from the California Avocado Commission on nutritional info:
I like their info a whole lot more than MFP, but they are biased.