Once upon a time people thought cameras were better if the number of megapixels was bigger, which is right up to a certain point, 12MP on a smartphone, somewhere 20–24MP on a DSLR.
What really matters is the size of the sensor’s pixel.
Now people think cameras are better if there’s more of them. Three cameras. Four cameras! Mine is bigger!
What really matters is to have two cameras so they can capture in stereoscopic mode, like your two eyes.
What really matters is to have two cameras with different focal lenses, as there’s no space on a smartphone for zoom lenses.
(ok, on this point it could potentially be worth to have more than two cameras, one for very wide angle, like a GoPro, one for 35–50mm equivalent (sees like our eyes see), and one for zoom, but that’s about it, because there’s no space for a bigger zoom)
So is Apple adding a third camera so they can be better because 3 is more than 2?
What Apple is adding is a depth sensor, similar to the one on the front, for FaceID. This sensor will provide proper depth information, instead of just trying to guess the distance by using the other two cameras.
This is why certain Android devices have three cameras, and it makes sense. They also have the wide and tele cameras, and then a black-and-white camera to help on the depth information. It’s not as advanced as the FaceID depth sensor, but it’s good enough and works quite well, if the software is well designed.
So no, it’s not a triple camera. You can call it a triple sensor if you want. Or if you want to call it a camera, be aware that the iPhone X* have two cameras in the front.