"VPN" is a generic term which includes various wildly different technologies (PPTP, L2TP, IPSEC, SSL...), whose common purpose is to access a remote network through the Internet, by creating a "tunnel" which lets a computer, or a whole network, talk to the remote network in a secure way. The basic idea is that a VPN can do the same job as a physical link, without the need to actually have that physical link built, by leveraging the independent Internet connections already existing at each end.
As you said, this is commonly used by employees to access the company network, or by companies to connect two geographical sites; but this doesn't mean VPNs can't be used by anyone for any purpose: VPN software is readily available in almost all operating systems and most consumer-grade routers; this is by no means an enterprise-only technology.
As to "why" they used it in this case... only they know. But as a VPN adds an additional level of security and encryption to any connection, it's quite understandable people concerned about security and privacy would use it.