Pressure in the proton, from gravitational form factors?

A paper in Nature is getting some press, for having calculated "the pressure distribution inside the proton".

But the theory behind the calculation seems a little odd. Apparently the data pertains to the scattering of an electron from a quark via the exchange of two photons. But each photon has spin 1, so that adds up to spin 2 like a graviton... and then there's talk about gravitational form factors, as if there are sufficient formal similarities with the two-photon electromagnetic form factors (?) that gravitational calculations can be transposed to the electromagnetic context.

I'm not at all saying this is impossible, but I am a little skeptical. Does anyone have an informed opinion on the validity of this work, and its methods?

BvU

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