In formal language theory, the exact definitions of terms tend to vary.
For instance, context-free grammars as introduced by Chomsky couldn't have empty right-hand sides. They couldn't produce the empty string. Quite a few articles followed this; later on, it became more common to allow this. Usually, the difference is of little or no consequence, but ...
This is rather surprising.
If we look at the specification of the Hack Computer, I found this (consistent with your query):
Instruction memory (ROM)
Data memory: Memory (RAM)
Also, I've been studying Computer Architecture- MIPS-64 bit by Hennessy, which is based on von Neumann's, like most of the general-purpose computers in the mainstream.
Harvard machines ...
I had the same suspicion going through the Nand to Tetris course.
Indeed, if you look at John K. Bennett's annotated version of "The Elements of Computing Systems", specifically Chapter 5, he calls this out:
The Hack architecture would more properly be called a “Harvard Architecture,” since the data and instruction memories are separate.
We can ...