The two cameras produce exactly the same image. I guess your grandma really is a bicycle.
It's exactly the same reason why 50mm f/2 lens produces the same image on a full frame camera as a 75mm f/2.8 lens on an APS-C 1.5x camera. It's just that instead of multiplying by 1.5 you're multiplying by 8.4.
Indeed an iPhone 13's ultrawide will provide exactly the same image and bokeh as a 13mm f/15.1 lens on FF
It's exactly the same reason why 50mm f/2 lens produces the same image on a full frame camera as a 75mm f/2.8 lens on an APS-C 1.5x camera. It's just that instead of multiplying by 1.5 you're multiplying by 8.4.
Indeed an iPhone 13's ultrawide will provide exactly the same image and bokeh as a 13mm f/15.1 lens on FF