Earlier quoted context omitted.
For the record, GCHQ created RSA in 1973 and then DH in 1974: * https://en.wikipedia.org/wiki/Public-key_cryptography#Histor... DH qua DH was invented in 1976, and RSA qua RSA in 1977.
What does qua mean here?
The concept "x" as we (generally) know x is what qua means. (Because words can mean and point to potentially many concepts.)