Electronic – a momentary SPST Push Button Switch

You apparently were looking for a push-on, push-off switch. What you got was a momentary pushbutton switch that's normally open.

As per my comment, the "Off-(NO)" position description is a little incorrect; it should be "Off-(On)" which simply means the switch has two positions, off and on, but the on position is momentary, thus in parenthesis.

The seller also describes it as "latching" which should mean that a single push changes its position, and it stays there until the next push. Technically that would mean it's also not momentary, so the description is contradictory.

I'd ask the seller for a refund or replacement. I frequently order non-critical parts from Hong Kong or Shenzhen, China via eBay and generally have good results. Most of the sellers from those locations are very concerned about feedback and maintaining a good reputation, so you should get an amicable response.

It's called a button. Button is something you push, knob is something you twist, in general.