They are measuring the distribution of energy within the proton. General relativity (GR) describes how a distribution of energy distorts spacetime. They could take these measurements of the proton (if they're complete enough) and compute its tiny effect on the curvature of spacetime with non-quantum GR. Quantum gravity only becomes relevant at the Plank length (~10^-35m) which is still much smaller than the proton radius (~10^-15m) or the resolution of their measurements.