The spinning is 2nd stage booster doing a "energy management maneuver", the spin decreases the final velocity of the KKV (basically it's a way to waste delta-V), you do it if the target isn't going fast enough to require the full capability of the interceptor. Some of the US ABM test you see this too, this is THAAD:
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Note that THAAD is KKV + 1 booster stage, this ABM test might be something like a "range boosted THAAD" with KKV + 2 booster stages. Hence why instead of doing the spin relatively close to the ground it does it much higher up shortly after 2nd stage ignition. The first stage probably doesn't have the maneouverability to do that as it's job is mainly to get the rest of the interceptor going fast enough and high enough.
In the context of this test the target vehicle might be a DF-21 or DF-4 with modified upper stage. Since it's not a full on ICBM like DF-41 or DF-5 the full capability is not required, hence the spinning.
It does show the interceptor is flexible enough to handle both ICBM and MRBM.