You're conflating many different things, all under the name "pixel". I think that's where your confusion is coming from:
> Cameras do not sample points
Cameras use sensor-elements (silver-iodide grains, CCD arrays, etc.). If you want to use the p-word, we could call them "sensor pixels", or suchlike.
> displays basically never have filtering to make pixels point samples
I don't understand what this means; displays are physical devices, which must have 3D extent.
In any case, we can call the display-elements of such devices "display pixels", to avoid confusion.
> most projectors literally project little squares
Again, these are display-elements (or "display pixels", if you must).
> This must have been written by someone that just learnt about sampling theory and thought "aha! Pixels are samples!" without actually thinking about real life.
The author is using the term "pixel" to refer to image data. That is not the same thing as display-elements, or sensor components, etc.
If you read it carefully, you'll see those examples are actually mentioned explicitly; along with e.g. the tone patterns used by printers.
Image data is recorded from sensor pixels (or rendered pixels) and displayed on screen pixels or pinted using ink pixels, without additional filtering unless the image is scaled or rotated. None of these are perfect pixels due to physical limitations but they all try to be mostly that: little squares.
It is convenient to think of image data as point samples because that lets you use sampling theory but that does not mean image pixels are actually point samples.
Or ro put it another way, if it's captured like a little square and displayed like a little square, it is a little square.
> Cameras do not sample points
Cameras use sensor-elements (silver-iodide grains, CCD arrays, etc.). If you want to use the p-word, we could call them "sensor pixels", or suchlike.
> displays basically never have filtering to make pixels point samples
I don't understand what this means; displays are physical devices, which must have 3D extent.
In any case, we can call the display-elements of such devices "display pixels", to avoid confusion.
> most projectors literally project little squares
Again, these are display-elements (or "display pixels", if you must).
> This must have been written by someone that just learnt about sampling theory and thought "aha! Pixels are samples!" without actually thinking about real life.
The author is using the term "pixel" to refer to image data. That is not the same thing as display-elements, or sensor components, etc.
If you read it carefully, you'll see those examples are actually mentioned explicitly; along with e.g. the tone patterns used by printers.