Maybe it’s only a question of semantics. Capillarization implies a shift white to red: by definition of capillarization, you have more capillaries, or more tortuous paths for the same capillary, thereby reaching more cells.
If CF-style tempo has benefits, then it could be because of the increased nutrient delivery as you are explaining. But increased-nutrient delivery can be achieved just with a program like Active Recovery (which by the way sweeps frequencies between 2 and 8 Hz).