Looks like it was split in two to provide the 1st floor flat with access to it's own plot via an outdoor staircase and a small corridor - which is presumably why a traditional side return wasn't an option.
It's meant to be a miniature wildflower meadow, it looks great roughly May-August but at this time of year it is a bit sad. It's never been as meadowy as I hoped for and the grasses have died back in some patches. Our tomatoes were a bit out of control then too.
Fucks sake. That garden.