I was always under the impression that suction fit this definition:
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A force that causes a fluid or solid to be drawn into an interior space or to adhere to a surface because of the difference between the external and internal pressures.
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So i'm perplexed when i hear that suction doesn't really exist because what's really going on is that fluids flow down pressure differential. To me it sounds similar to making a claim that frictional forces don't exist because what's really going on is shear stress due to the breaking of the microwelds that form at asperities between two materials in contact. We generalize it and call it friction because its convenient. How is suction different? Going a step further, you could claim that the "pressure gradient" explanation is wrong too, because pressure doesn't actually exist- it's just a macroscopic approximation for interactions between different particles.
The test was poorly worded, it happens.