I was following the sizes listed here, and I've been creating the artboards with the sizes in points, but should I be creating them with the size for rendered pixels instead? Furthermore, I believe Sketch use points but correct me if I'm wrong.
As the page you linked to says, the point units are an abstract system for determining coordinates; they don't directly correspond to pixels on a screen but give a convenient coordinate space across devices; so you can have an icon that is always 40 × 40 pt even though it is rendered at different pixel sizes on different devices.
If you're creating raster images (i.e. made of pixels at a specific size) then you want to make your images at the actual pixel size of the screen. Namely;
- 320 × 480 pixels for original iPhones
- 640 × 960 pixels for iPhone 4/4S
- 640 × 1136 pixels for iPhone 5/5S
- 750 × 1334 pixels for iPhone 6/6S/7
- 1080 × 1920 pixels for iPhone 6/6S/7 Plus
The reason Sketch would (I assume, I don't actually use Sketch) use points is because it works with vectors. If you're working exclusively with vectors then all that really matters is the proportions of the image; so you can work in points (or any other size/unit in the correct proportions; points are just convenient) to create assets to be used across multiple devices and output at the correct pixel sizes when needs be.