I usually interpret this as behaviour: photons are not "particles" or "waves", photons are photons. They just behave as waves and as particles, depending on how you're looking at them.

Note that even things with a resting mass (like you or me) are like this, too. It's just that, as the mass increases, the wave behaviour becomes negligible.

The crazy thing is there are actually two double slit experiments, and that light can tell whether or not you are actively observing it or not, and decides whether or not to actually exist as a wave or particle.