Intel 8080 was launched in April 1974 and the development system for it, "Intellec 8 Mod 80", was available soon after that.

CP/M could be developed only after the launch of the 8080 and the delivery of the development system.

In UNIX, the environment variables were added in the Seventh Edition (1979-01), together with the Bourne shell.

I do not remember whether any other command interpreters used something equivalent with environment variables before the UNIX shell (excluding the interpreters for general-purpose programming languages, like LISP and APL, where you can run a function in REPL and that function can access global variables).

Therefore the quoted year may be a typo for 1979, when environment variables appeared in the UNIX shell, but were not available in the CP/M Console Command Processor (CCP, the predecessor of COMMAND.COM).