Well, at a quick guess, and quicker google, I'd guess that the yeast is a champagne type yeast.
So while 1125 is quite a high starting gravity, according to the reference chart I use, there's a "suggested" strength of just under 17% ABV if it fermented dry i.e. to 1000.
Now I know that normally a gravity that high on starting would need a little extra "management" during the earlier stages of ferment, but it's possible.
Of the quantity, 4kg/8.8lb of honey is a hell of a lot, so I'm thinking that it might have been quite a "mediocre" honey - with quite a high water content. Because 8.8lb per gallon would normally create a gravity a lot higher than 1125.
Anyway, Joes ancient orange recipe is designed to be made with bread yeast as there's supposed to be some residual sugar in it. It's entirely possible to have a bread yeast ferment dry as well, but that doesn't usually happen (and there's little to no data about the alcohol tolerance of bread yeasts).
If you're sure it's finished the ferment i.e. you get the same gravity reading on 3 occasions - each measurement a couple of days apart, then what the hell, make up a honey/water solution, something like 2 honey to 1 water and add that until you reach the desired taste or gravity level (I don't enjoy meads that are cloyingly sweet, so aim for about 1020 finished). Don't forget that with a tolerance of about 18% with that yeast, you'll have to sulphite and then sorbate to prevent refermentation - unlikely but possible.......