Notice the format of the hostname: ::ffff:a.b.c.d

I had to look this up: this is a IPv4-mapped IPv6 address. It is a format to describe an IPv4 address using a IPv6 address format.

From Wikipedia article on IPv6 addresses:

::ffff:0:0/96 ? This prefix is used for IPv6 transition mechanisms and designated as an IPv4-mapped IPv6 address.

With a few exceptions, this address type allows the transparent use of the transport layer protocols over IPv4 through the IPv6 networking application programming interface. In this dual-stack configuration, server applications only need to open a single listening socket to handle connections from clients using IPv6 or IPv4 protocols. IPv6 clients are handled natively by default, and IPv4 clients appear as IPv6 clients at their IPv4-mapped IPv6 address. Transmission is handled similarly; established sockets may be used to transmit IPv4 or IPv6 datagram, based on the binding to an IPv6 address, or an IPv4-mapped address.

The IPv4 part of the address can also be represented in hexadecimal: ::ffff:aabb:ccdd