Good question! 'Sucking' here is a bit like 'centrifugal force' - it's a real thing, but only in the right frame of reference.

In the case of centrifugal force, it's a real thing in a rotating reference frame, but doesn't exist in an inertial reference frame (because in that frame the acceleration is towards the center, ie. centripetal).

In the case of suction, it's a real thing when your zero-pressure reference point is above 'absolute zero' pressure, such as when you're measuring gauge pressure. In this case you can have an area of 'negative pressure' which is 'sucking' the surrounding fluid into it.