There is "RSA" as implemented by GCHQ in 1973, and there is "RSA" as RSA like we generally know it by the three folks that it was named after. There is "DH" as implemented by GCHQ in 1974, and there is "DH" as DH like we generally know by the two folks that it was named after.

The concept "x" as we (generally) know x is what qua means. (Because words can mean and point to potentially many concepts.)

I'm assuming "by": as in those algorithms were created by the people whose names are now associated with them in those years

"as"

He means DH, as in Diffie Hellman, was not the first approach to key exchange. The difference is that in the UK we did what we usually do: we squandered an amazing innovation and let some other country benefit from it.