It's not ionizing. It'd be impressive (and probably highly illegal) if it was. The "radiation" was below the range of visible light (technically, visible light is a form of radiation), meaning it's fairly low energy. In order for it to increase your cancer risk, it needs to be above the visible light spectrum (ultraviolet and higher), otherwise it lacks the energy to damage cells directly. Their use of the term "radiation" is hard-core clickbait.

Radiowaves, microwaves, infrared, visible light, ultraviolet and x-rays are all radiation, and they're all light. If you had the right tools, you could theoretically take a picture using only microwaves and/or radiowaves. Additionally, radiowaves and microwaves are below the visible light range (so they don't cause cancer) and require a ton of power to cook something (microwave ovens are usually +1000 watts, iirc the iPhone was putting out slightly more than 5 watts in the radiowave range, which afaik requires more power to cook something).