The obvious possibility is because Arday said so, and Afzal and Cambridge believed him. I don’t know that with certainty, but likewise neither you nor Vixen know any other basis for his claim. And even if that’s in his file, we don’t know if it’s in there because Cambridge HR believed Arday or because they got their hands on a formal diagnosis.
But given both Arday’s history of lying and Cambridge’s history of believing his lies, there is no reason for any of us to simply take Afzal’s statement about Arday having autism as true. Either that traces back to a formal diagnosis, or it doesn’t. If it does, that’s what we need to see, not Afzal’s word for it and not even HR’s word for it. If it doesn’t, the claim is worthless.