The blog link describes the cleanup process.

They take two pictures, each taking up half the total observation period. If you subtract the two images, the deltas should be the cosmic ray flashes. You can then subtract those out. They use two pictures as opposed to more to minimize the impact of readout noise.

To deal with "stuck pixel" type errors, they can slightly shift the camera between the two observations. They can counter act the shift before doing the initial subtraction.

Signal processing / denoising of astronomical images is a field of study onto itself.

If you are like me you will find it super interesting. There is immense variety based upon what kind of telescope, what do you want to capture, whether it's for science or astrophotography (aesthetics).

If you are into math side of things you can begin with Richardson-Lucy as a starting point and stacking.

funny how this also eliminates "close" fast moving objects. which I guess is a feature for a telescope