I think that's kind of his point - Optionals/tagged unions are "Null values", but only in the places where they semantically make sense.
The problem with nulls isn't strictly null references, in the sense of "a pointer that points to nothing" or "a pointer that throws a null pointer exception", it's that languages with nulls implicitly make null an element of every type. They tend to do this because variables are allowed to have null references, but if you changed the semantics of variables to technically forbid null references, but still had a null value as an implicit element of every type, you'd still have the problem of needing to do runtime checks for null everywhere.
The problem with nulls isn't strictly null references, in the sense of "a pointer that points to nothing" or "a pointer that throws a null pointer exception", it's that languages with nulls implicitly make null an element of every type. They tend to do this because variables are allowed to have null references, but if you changed the semantics of variables to technically forbid null references, but still had a null value as an implicit element of every type, you'd still have the problem of needing to do runtime checks for null everywhere.