The languages Oberon and Oberon-2 were explicitly designed for the task of creating the operating system Oberon. When Wirth started working on the OS he realized that it would be too hard to write a nice OS with just Modula-2 (at least that's what I understood from the interviews he gave with various journals). Modula-3 was an evolution of Modula-2 by DEC (not by Wirth), but it was influenced by Oberon and they all belong to the same "Pascal language family" in terms of design philosophy.
I think it's very natural to mention Modula-3 in the context of Oberon.
I think it's very natural to mention Modula-3 in the context of Oberon.