I have a son who has extreme anxiety, and kept getting referred by teachers for ADHD. Hyper-vigilance for danger can make it hard to focus on arithmetic, particularly in an elementary school classroom. The psychiatrist ended up putting a note in his file because this was happening.
Meanwhile, I also have a daughter who is so obviously ADHD: she forgets to turn in her homework; there were 6 of her jackets in the lost and found in October; she will go to school without her eyeglasses; &c. But, she doesn't disrupt the classroom and is otherwise seen as a "good kid" so she was never referred by a teacher.
I really suggest some sort of setup to maintain structure as she gets older - being aware of a diagnosis or having medication / therapy would've really saved a couple painful years in university for me
The wisdom you're referencing is circa the 70's, it's been attempted many times since and has never replicated.
Also your framing ignores that the "prompting" can be circumstantial rather than targeted. The "rush" is frequently misattributed to sugar when it can actually be better explained by the food itself being a rare treat (and thus exciting) or the situation in which it is provided being special (e.g. a party). Or it can simply be the joy of eating something very tasty.
It's less Clever Hans and more "kids are more prone to sudden outbursts of strong emotions and adults blame it on food".