I also thought it might've been about the differences between them, given that Pashto has its own characters unique to its script and Arabic has diacritic marks

I also thought it might've been about the differences between them, given that Pashto has its own characters unique to its script and Arabic has diacritic marks not used by Farsi or Pahto. This is a different subject, though, that has little to do with what the post is complaining about. Their grievances apply to all scripts based on Arabic.