someone on my team asking personal questions about my disability exemption

my manager who is aware of my exemption is out on disability indefinitely so the acting manager is who i’m in communication with for the time being. i had to miss a meeting for a medical issue and needed to reschedule it to later today and the guy is asking me what’s wrong with me that i can’t take the meeting right now and to send proof my disability. am i crazy or do i not have to disclose that to him? i feel like it’s so unfair to even ask me that