I am not sure about those symptoms, but it can lower the blood sugar in 2 ways, by speeding the metabolism, and by them just not eating.
The frequent urination is only one sign of Diabetes, and not a huge one....I am diabetic. It wouldn't hurt to have his Psych check his blood sugar, and maybe order some blood work.
A child may HAVE ADHD, but it is not what they ARE. Never tell a child they ARE ADHD.