I’m not a physicist, but I think the comparison is made between gravity and e.g. strong nuclear force. In the latter, the “force” is modelled by interactions between hadrons, with virtual particles (distortions in various fields) mediating the interaction. With gravity, there are no particles (though graviton is a hypothesis).

One can say that space time is also “field”, and mass creates distortions, so gravity is just like other forces interacting via field distortions, but iiuc, unlike nuclear forces, gravity does not have a quantized mathematical model.