Electric charge is not like a number chiseled in stone. In the vacuum around any charged particle, pairs of particles and antiparticles are constantly born and annihilated, like the foam in a glass of champagne. The bubbles screen the true charge, making it appear smaller or larger depending on how close we get. This effect is known as the running coupling constant.
The authors used lattice calculations — a method where spacetime is replaced by a crystal-like grid, and quark and gluon interactions are computed step by step. This allowed them to achieve precision at the tenths of a percent level where uncertainty once reigned. They then combined these data with high-energy theory, like two pieces of a map finally fitting together. The result is a new value for the electromagnetic force at the scale of the Z boson (the particle that carries the weak force). This number—0.027821—is now known with an uncertainty smaller than the thickness of a human hair compared to a football field.
The difference between the 'bare' charge of the electron and what we see in experiments is about 0.1%—roughly like your weight on a scale changing by 100 grams depending on whether you stand on tiptoes or flat-footed.