None of these….pausing flow could be a bloom phase and can be pressure independent. Pre-infusion is means to be infusing the puck for a period at a lower pressure than you intend to use for the final shot . As in the E61 pre-infusion chamber…although it’s a very shot pause. Or like an Evo which might pre-infuse for6 or 7 seconds at 2 bar…or even longer.
The whole point is to gently infuse the puck before the higher pressure compresses it,,,This infusion, also seems to prevent/resist extreme compression and gives a more even flow, even allowing use of a finer grind..