If backslash simply means "not the default", then its meaning varies with your expectations.

I'm thinking that it more-specifically means "take it literally, not as instructions to find the answer.". Then you get this progression:

foo => &bar means call bar now when the structure is being built. foo => \&bar means call bar later, when foo is imported (and bar can see the context of what the impoter is asking for). Finally, foo => \\&bar will call bar even later, when foo is actually called after being imported.

—John