You're making a very interesting distinction between the experimental result, which is that antimatter follows the same space-time curve as normal matter, and the dashed hope of warp drives, which is that antimatter causes the same space-time curve as normal matter.
However, if antimatter were to create a negative curvature but follow positive curvature, then you would be able to put a lump of normal matter next to a lump of antimatter, connect the two together, and the whole mechanism would spontaneously accelerate forever, breaking the laws of conservation of energy and momentum. For that reason, I think this experiment also gives us high confidence that antimatter causes exactly the same space-time curvature as normal matter, even though we haven't gathered enough antimatter to see it creating a normal space-time curvature. In essence, gravity is symmetrical.
However, if antimatter were to create a negative curvature but follow positive curvature, then you would be able to put a lump of normal matter next to a lump of antimatter, connect the two together, and the whole mechanism would spontaneously accelerate forever, breaking the laws of conservation of energy and momentum. For that reason, I think this experiment also gives us high confidence that antimatter causes exactly the same space-time curvature as normal matter, even though we haven't gathered enough antimatter to see it creating a normal space-time curvature. In essence, gravity is symmetrical.