I agree with shaggy. I don't know how you would expect to have a VPN accessible only by your account's droplets for $5. A private network means an internal network. So it's just using the internal infrastructure of the data center to communicate with other droplets in the data center. It's more performant than using the external network. Usually companies' advertise a fully private account infrastructure as a "Private Cloud" or something of that nature.
"Private Network" is often analogous with "Internal Network". They aren't lying,it's private as in it's using private IP assignment within their own infrastructure. Thus, private.
