Light is neither

I would agree that light is neither but Feynman is very adamant that it's a particle and he describes all the properties of light using a particle only model. It's much simpler conceptually to keep everything as a particle than treating light as a wave that sometimes collapses to a particle.

In his book he used the Mayan numbering system as an analogy. You can do everything in math by counting one by one, it's only extremely cumbersome. In a similar way he saw waves as a mathematical method to make calculating particles easier in some situations. But underlying the fancy math, it's still counting one by one.

Feynman argues that you can calculate and observe everything as only particles but you can never observe waves and have to make waves instantly transform into particles if you treat them as waves.