They have the same amount of carbs as ordinary spuds, but are lower GI so take longer to disperse all their glucose. Also the fat from the frying will have helped. I have never tried sweet pots but I am fine with normal chips - in small quantities - if they are deep fried. Perhaps try some additional testing at an hour, 2 hours, then every 30 minutes thereafter until you return to base.
7.8 at 2 hours is not a figure to aim for. It is an absolute maximum, ideally a lot less.