It's been shown that ketogenic diets - where whole body and brain switch to fat/ketones instead of glucose for power helps with Epilepsy (and was it also Parkinsons).
To force your body into a purely ketone metabolism, you'd need to restrict not just carbohydrates but also protein. If a person is eating a high-fat, high-protein diet, their body will make glucose/glycogen from that.
Not to say there isn't value in a low-sugar diet. There's a whole cascade of other things happening metabolically in response to blood sugar. Just that the notion of "burning ketones instead of glucose" is a medical myth, like "depression is because you have too little serotonin in your brain".
That is expected and fine. It wont make glucose/glycogen in the same way/manner it would do from carbs though, and it's not really a problem for getting into ketosis and staying there (as shown by ketone measurements).
That professor was making a pedantic argument it seems.
AFAIK they usually form ahead of ketogenic diet - when people are eating little fat and dont need much enzyme/bile - it's not flushed from gallbladder often enough.
And then increased fat consumption on ketogenic (or Paleo, Mediterranean, Carnivore ...etc) diet requires flushing gallbladder - and only then you realize you have gallbladder stones.
Anyway - true ketogenic diet is hard to pull off and maintain. Even just few glasses of milk (~2.5g of carbs per 100ml) could take you out of ketosis.
Same for basically any typical fruit (e.g. apple, pear, orange, banana...etc) where one fruit is enough carbs to take you out of ketosis.
So it's more realistic to sustain low carb with <=50g of carbs per day, and get most of benefits (including weight loss without increasing exercise) without too much risk of all the mentioned negatives.
Of course YMMV, and you should consult at least your GP (or other specialists) before changing your diet a lot.
In personal experience - such low carb diet works nice in combo with skipping breakfast (not quite intermittent fasting, but time between first and last meal is shorter than time from last meal until next days meal).
If anyone is like me and can't really skip breakfast, nor at least delay first meal until noon.
I've found drinking "bulletproof coffee" takes case of hunger and energy until actual lunch time.
Despite media hype it can be just water, coffee - instant or grounded Turkish/Greek/Balkan style, espresso isn't enough liquid for full mug - with butter and coconut aka MTC oil.
And of course if such coffee doesn't work for you as meal replacement. Then eggs, bacon/sausages, avocado (no bread, no beans, no orange/apple/etc juice) is a perfect (practically 0 carbs) meal that works for breakfast, brunch or dinner.
And through bypassing damaged or suboptimal glucose pathways, you also bypass problems that come with it.
Of course it might also be that ADHD brains simply do come from evolution of what used to be Hunters (as opposed to Gatherers). It wouldn't be too unreasonable to think Hunters ate more fat and protein than Gatherers.