That may be true. The USDA says that anything over 18% can ferment, and anything over 19% will ferment.
Take this FWIW, which is basically a person with limited knowledge and no real formal education on the subject, but....
From
THIS link here on Beesource you can see there is a wide range of the various sugars found in honey and this is really only comparing a couple different honey's.
Fructose, listed as Levulose...don't ask me why sugars have ten different names for the same thing...has about 6-7% higher density then glucose, listed as dextrose. Since each degree of Brix is a measurement of 1g of sucrose in 100g of solution you would probably, not sure, get a different reading for 1g of fructose in a 100g solution then 1g of sucrose in solution.
Since moisture content readers for honey are the inverse of the Brix, meaning 20% moisture content is actually 80 Brix, if you had a 100% sucrose mixture vs 100% fructose mixture I would think you would be getting 20% moisture with 80g in 100g solution of sucrose but would be getting 14% moisture level with 80g of fructose. I'm guessing this because succrose is more dense then sucrose and thus the same one gram by weight has more particles which I would assume would increase the brix and thus lower moisture content.
IOW it would not surprise me at all to see one honey with 20% moisture content and another with 18% moisture content that both contained the same solution by weight. Again this is largely a guess though.
~Matt