It's not G.fast. It supports VDSL2 profile 35b, also known as "SuperVectoring", which uses frequencies up to 35MHz. The operators in some countries decided to upgrade their FTTC networks with profile 35b / SuperVectoring VDSL2 equipment, Openreach opted for G.fast instead.
The RJ11 VDSL2 socket appears to have 4 pins, so it would be quite simple to have one line wired to the inner pair of pins, and another line wired to the outer pair of pins. The technical data
does say "Y-cable for bonding connection".