This article seems to miss explaining one of its statements.
If a proton is made up of 2 up and 1 down quark, and a neutron is made up of 1 up and 2 down quarks, and an electron is not made of quarks, but is instead another elementary particle, then now do neutron stars compress protons and electrons into neutrons, and how do atoms that beta decay emit an electron while turning one of the neutrons in the nucleus into proton?
One plausible answer is that they are all made of even smaller particles, but that is speculative. See https://www.quora.com/Are-electrons-made-from-quarks
where one answer says:
"In the Standard Model of particle physics, quarks are fundamental particles. So no, they do not have smaller constituents.
"It is, however, possible to go one level deeper mathematically, while preserving all the desirable symmetry properties of the quark picture. In the so-called preon model, all the known fermions: leptons like the electron and its neutrino, and quarks, are composite particles made up from different permutations of two preons, one neutral, the other carrying 1/3rd unit of electric charge.
"However, it must be emphasized that this is a purely speculative model with no experimental support whatsoever."