No. The cross-sectional area is the area perpendicular to the direction of current flow, through which the current is flowing. If the current were flowing axially through a solid cylinder of radius r, then the cross-sectional area would, indeed, be pi*r2, and it would be constant all the way along the cylinder. However, here the current is flowing radially outward , so the cross-sectional area gets bigger as you go further out from the centre.
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