> Doesn't that make this a bit pointless since I don't know anyone that [...]

There is a very large variety of people out there. It's unlikely that your social bubble contains all the different ways to use a phone. if you search the net the phrase "phone clearing dump" you will find example of people having filled their phones with so much "funny images" that they are now saving them to an online image hosting service.

You probably also don't know anyone who has depictions of sexual abuse of children on their phones, yet it is a thing that exists, and that apple seems to be trying to address.

The world is big and, as you say, weird ineed.

And a sub-question: doesn't that make this ideal for checking for copyright infringement instead?

copyright enforcement, detecting terrorists, sussing out dissidents. The applications are endless!!! Welcome to the future.

yes. it's specific images. It's pointless and looks half-assed, but hey, they have the future to perfect it. This is only the watered down/tame version to get the foot in the door and cause a big commotion while still being able to keep plausible deniability. Once they do this a couple of times people will get tires and stop caring. That's when the scary stuff slips in.

It finds specific images, but the hash is based on pixels, not raw file bytes. The hash is insensitive to small image changes (brightness, saturation, rotation, compression artifacts), so slightly modified images still hash to the same value.