Why is the nitrile nitrogen sp hybridized?

[![enter image description here](https://i.stack.imgur.com/ONHDQ.jpg)](https://i.stack.imgur.com/ONHDQ.jpg)


This [site](http://www.meta-synthesis.com/webbook/40_polyatomics/polyatomics.html), from which the above image was taken, indicates that the hybridization of the orbitals on the C and N atoms in hydrogen cyanide is sp. I can certainly see how that would be the case for carbon, but why need the terminal nitrogen atom have sp hybrid orbitals? Couldn't it form a σ bond with the carbon's sp orbital through its s or p orbitals and use two other p orbitals to form the two π bonds?


