Thanks for the link to the Vic Road Rules 2009.
This probably serves as a good example of why we should all exercise a little more discretion and caution when dealing with the rules in other states. To use my analogy this is a better assembly of the pieces of paper than I found although I do find the dictionary at the back, being the definitions which then refer to specific rules for the definition having come from another definition for that same one very confusing and requiring multiple copies open to track.
Can you give me the road rule number that covers this rule? It's just that I have never seen it mentioned
From the link you provided this is Rule 250 (2) (a) - very clear and black and white.
Furthermore riding more than single file, except to overtake, is covered in Rule 151 (1) and, if you think that does not apply to shared paths then Rule 151 (5) clarifies that.
Although rule 151 says that when two abreast this is max 1.5m apart, does this only apply to overtaking and my homework to you sir is: Can you tell me which rules that actually permit riding two abreast on the road? Now there is another can of worms.
At least in WA we are explicit when we can, on the road, and when we can't, on a shared path.