Why is oxide of a non metal called basic oxide?

1. Basic oxide is an oxide that produces bases when they are combined with water.
2. Non-metal oxides when combined with water produce a base as a product.

For example;

${\mathrm{Na}}_2\mathrm{O}\left(\mathrm{s}\right)+{\mathrm{H}}_2\mathrm{O}\left(\mathrm{aq}\right)\to 2\mathrm{NaOH}\left(\mathrm{aq}\right)$

Therefore, oxide of non-metal is called basic oxide due to the formation of the base.