Not a cryptographer, but I wonder if some sort of basic statistical fingerprinting of the private key being checked at every step of its manipulation during the ceremony would have caught this epic operational failure.

Say, like a multi-scale hierarchical half popcount vector (first/second half, first quarter+third quarter/second quarter+fourth quarter down to odd/even bits), where fumbling one private key for another or xkcd-ing 4 as a private key would be detected, but still reveal no information on a truly random series of bits and be understandable by non-technical people in the room.