The resentment of Afghan Pashtuns towards Pashtunkhwa Pashtun is primarily due to the reason that majority of Pashtunkhwa Pashtuns have developed sympathies with Punjabis and serve as loyal servants to them, which makes them less Pashtuns since they have started eating more daal, lolx. Not to forget how ISI used Pashtuns of Pashtunkhwa against Pashtuns of Afghanistan. So it makes sense why would not they be angry with Pashtunkhwa Pashtuns. I am sure you have thousands arguments why you are angry with them