It's actually quite odd. I noticed that there's a misplaced bracket there so thought perhaps there was an error there that hadn't been corrected.
Jacket potatoes are one of those things that used to be assumed to be slow acting because of the skin, yet when they tested!. It definitely isn't low GI unless it's loaded with butter, cheese , sour cream etc
On the dietary advice page they write about low GI and in one point have a list which rightly incudes boiled new potatoes yet on the same page the jacket potato get another mention :!: