This
This is not to argue against the advice you have been given, but rather to supplement it. Don't try and perfect the motion from the descriptions of it only on its own and expect the sound you want to come out the other end; consider the sound you want and use the ideas presented above in your playing in order to produce the sound you envisage. Use that sound as your guide to finesse the movements.
Your ear will be the one that will tell you if you´re doing it right or wrong, or if it´s missing something. No matter what you have to do, if it solves the music, it works; and if it doesn´t hurt you of course

. Another thing I´d like to add, my teacher always reminds me when playing non-legato to think as if I´m pulling up my fingers, not pressing down the keys; of course, in reality you are moving downwards your fingers but the point is the sensation of pulling up quickly, almost just by keeping that in mind you automatically start getting the non-legato articulation.
And about GG´s use of legato and non-legato, or stacatto, I was taught as a point of reference, not as a rule, to use legato with short intervals, specially seconds, and as they get bigger (thirds, 4ths, 5ths, octaves) you would start changing to non-legato, etc. The thing with articulation has to do with the baroque rhetoric and symbolism, like for example, a minor second represents sadness and that´s why you play them legato etc. (Sorry, I´m not trying to be accurate since I really don´t have the knowledge fresh, I have to consult sources again) That´s the reason why Bach´s music rarely has any slurs or articulation marks, because they had like this reference or code so they automatically knew if it was needed to be played legato or non-legato, etc. making the action of writing it down a limitation. Articulation as well as ornaments could also be improvised during the performance.
Listening to Glenn Gould I also learned it serves as a contrast. In a fugue, for example, a way to differentiate each voice is by playing each of them with a different articulation, or even play the theme with a different articulation every time it appears so you don´t repeat the same thing twice, let´s say the first fugue of the first WTC, you start with the first 4 seconds legato, then on the second voice you play those 4 seconds non-legato, etc.
The point is that the possibilities are practically infinite, and if it solves the music it works, so experiment with the possibilities. It´s not just black and white.