If the course of study - even a 'short' course results in some form of certificate or qualification etc then it requires the appropriate visa. If the study is such that it does not result in a certificate/qualification then the status quo applies. However, as you see, Flight Training is specifically called out as an example in that letter and makes no reference to what is deemed a short course. The fact that it results in a qualification is what matters.
I fail to understand why folk make such a big deal of getting a visa - it costs around $300 which in the grand scheme of flight training is a drop in the ocean.