I dunno if it's bad translation, or if he's just plain incorrect, but the progression you wrote out is certainly still C-centric at that point. Listen to it.
I barely even know what you're talking about. Not every V–I is a cadence; cadences are at the ends of phrases. You can have cadential progressions in the middle of phrases, but these aren't cadences, because they're in the middle. 'Non-cadential cadence' doesn't make any sense; it's like saying 'the green red chair'. If a phrase ends with a cadence in a new key, it has modulated; if it uses an applied dominant or cadential progression in the middle, it's tonicizing.
If you play your C–G/Bb–A7–Dm progression, but don't have a C# in the A7 (i.e., the chord would just use A, E, and G—maybe in just two or three parts), it still tonicizes D minor, because of the root progression: