I am also struggling to understand if I need a visa just to do a Night Qualification in USA (some say that it is considered training if the training exceeds 18 hours).
So I looked into the Code of Federal Regulations where it says something about the 18 hrs but it is so complicated that it is not clear.
I decided the the risk of having troubles in the USA it is not worth it and I will spend 200$ and some hours at the embassy to get the VISA.
My advice is: if it is training than you need a VISA.
Cheers