40 units isn't an amazingly low TDD. To work out the average TDD for weight multiple you weight in kg X 0.53 so for you = about 60 so your TDD is below average, perhaps because you are very active.
A low HbA1c does not indicate misdiagnosis - it suggests you have good control. Sounds like the hypos are occurring in connection with an increase in activity.
If they really suspect misdiagnosis the first step should be cpeptide and gad testing.
Even then, frankly, a "misdiagnosis" isn't going to have made a blind bit of difference to your treatment/management or prognosis - you obviously need the insulin (40u isn't an insignificant amount) to keep in good control.
If it was your GP practice nurse, I'm going to suggest she was just not used to seeing type 1 s with such good control & her misdiagnosis theory is unfounded and reflects a possible lack of experience.