This fatwa is based on a hadith reported by Hazrat Aswad from Hazrat Aisha. She said that she used to scrape semen from the clothes of the Prophet ﷺ, and then he would pray in the same clothes.
Based on this hadith, Islamic scholars of the Shafii school say that human semen is pure. Because of this, if someone prays while wearing clothes with semen on them, the prayer is valid. This is the Islamic ruling mentioned by scholars like Imam Khateeb Sharbini.
This fatwa clearly shows that, according to Shafii Islamic scholars, the prayer is correct in this situation.