It's worth reading about, but it's kind of wave-like even then: https://en.wikipedia.org/wiki/Double-slit_experiment#Interfe...
It would be going too far to say it's only a wave though. It's both wave and particle.
The way I read GGP was as contradicting the assertion that everything is just waves and not at all particles.
The way I read GGP was as contradicting the assertion that everything is just waves and not at all particles.