Author here: Thanks! The 1 instruction will place the opcode received from the serial line or the keyboard to a fixed location in memory. Maybe store would be a better name. But store (!) in Forth is associated with a memory address.
The compilation term comes from the fact that at the end the memory map will be the same as the one compiled with an assembler.
Also in the Frank Sergeant 3 inst version. Load is used to load a memory address on the target and send it back to the host computer.