Why is ionic bonding referred to as non directional?

is non-directional because an ion has the same attraction from all directions for an ion of opposite charge.
In the same way, a magnet attracts iron filings from all directions.
This means that packing efficiency in the crystal lattice determines the arrangement of ions in a crystal.
There is no preferred direction for the bonds.
Thus, in a crystal of ##”NaCl”##, a sodium ion has 6 chloride ions as nearest neighbours.
The ##”Na-Cl”## “bonds” are all at angles of 90° to each other.
In a crystal of cesium chloride, a cesium ion has eight chloride atoms as nearest neighbours.
The ##”Cs-Cl”## “bonds” are at different angles.
The differences arise because ##”Cs”^”+”## and ##”Cl”^”-“## have almost the same ionic radii (about 170 pm) and pack in one arrangement.
A ##”Na”^”+”## ion is smaller (116 pm) than ##”Cl”^”-“##, so the ions pack in a different arrangement.