I would call it "non-standard".
That grip was popular a few years back...but it has fallen out of favour now.
The best way it's been explained to me on getting a good grip is this:
Strong hand as normal.
Extend arms.
Open support hand, fingers together, thumb vertical, fingers horizontal.
Rotate hand downwards to approximately 45 degrees.
Wrap it around your strong hand.
Both thumbs point forward.
This should allow maximum contact. It feels awkward at first but eventually becomes so natural you will forget everything else.