Their point is that you can always give your number to anyone and they can directly use it to contact you. It's never unclear what number to give someone so they can reach you. Yeah calls have to be routed, but routes are implicit, not something you have to worry about as src or dest.
Say you're at home, you have a landline, and you don't know what your own phone number is. How do you get it? You call someone with caller ID, and ask them to tell you what number you called from.
There are numbers one can call for ANI / ANAC info from a landline. They vary by carrier and sometimes region. MCI has a well-known line that reads back your number.
Of course, I haven't had a land line in years and my cell phones tell me their numbers in the settings.
I'm referring to the fact that people don't know their own phone numbers, and instead of reading it, they'll call you and the receiver sees the number.
Their point is that you can always give your number to anyone and they can directly use it to contact you. It's never unclear what number to give someone so they can reach you. Yeah calls have to be routed, but routes are implicit, not something you have to worry about as src or dest.