I think this is more about the terminology than the actual concepts. This is like in biology, where you classify things as living and non-living, but then you encounter things like viruses, which would depend on the criteria for a "living thing." Or, is a gel a solid or a liquid? Again, it has properties of both states of matter. Similarly, in order to classify phenomena as waves or particles, you look for common attributes between the things you observe. But light exhibits properties of both.