Well, Lisi E-8 is about fundamental particles. A meson is combination of existing fundamental particles, quarks. Lisi is predicting some new fundamental particles.

An electron is a fundamental particle, of the "lepton" class. A proton and a neutron, however, are not fundamental, but made up of quarks, which are fundamental.

Here is a Wiki primer on the elementary particle zoo:

http://en.wikipedia.org/wiki/Elementary_particles

ETA: E-8 is about "how they go together" too. So I guess E-8 should say this 4 quark meson is "allowed". Heck, I don't know.

-Richard