Yes, most shells do not have a concept of a list (for variables).
That is not a defined type of content (separate from string or number).
However, the parameters of a command are a list.
That is a very special kind of data type, one that only
"$@" would express as a list. But with differences:
$ set -- one two t33
$ printf '<%s> ' "$*" ; echo
<one two t33>
$ printf '<%s> ' "$@" ; echo
<one> <two> <t33>
$ for s; do printf '<%s>' "$s" ; done; echo
Having explained that, what the quote means is that a list of parameters with 0 elements is equivalent to a list with no elements.
The last code prints "nothing", not even an "empty" (null) string.
So, about your question:
Can "nothing" mean something which is not necessarily a "list" or array?
No, "nothing" is necessarily a (empty) "list".
However, a "null string" is something.