Why would a plane perform 360° turns to balance fuel on the ground?
They probably had a fuel imbalance that was marginally outside the limit for takeoff, and perhaps the powered fuel transfer system was unserviceable and was deferred.  Typically there is a gravity transfer capability by just opening a transfer valve and letting fuel run across on its own with the imbalance present, or by skidding slightly.

If they were say 50 or 100lbs above the max lateral imbalance for departure, a spin around on the ramp a couple times with the gravity transfer valve open so that some fuel "sloshes" through the gravity transfer line to the opposite tank, due to the centrifugal force of the turn, may have been enough to get the value in limits.