It's articles like this that make me want to scream.

[davidb]

https://arstechnica.com/science/2017/05/the-mongols-built-an-empire-with-one-technological-breakthrough/

Now people will think that the Mongols invented the metal stirrup, invented steppe warfare. 

[John GL]

So that's why it's called a "Parthian shot".  Err...

[Imperial Dave]

I was amused by the puntastic website name......just me? Oh, I'll get my coat 

[Patrick Waterson]

I was amused by the puntastic website name......

They do appear to have difficulty distinguishing their ars from their [composite]bow.

As John G-L mentions, the tactic mentioned was popularised by the (stirrup-less) Parthians; the stirrup seems to have been invented by the Avars, both of whom precede the Mongols by a few centuries.

[Duncan Head]

the stirrup seems to have been invented by the Avars

Brought west by the Avars, anyway. Possibly invented by the Xianbei a few centuries earlier. There are some even earlier Indian and Kushan representations, but they may all be leather loop stirrups or open "platform" stirrups rather than solid loops.

[Dangun]

I think they start showing up all over the place in China's archaeological record from the third century.

Isn't the stirrup a paired technology in that you have to go to hard saddles or it doesn't work?
(I seem to remember something along the lines of the horse not liking soft saddle/stirrup combinations.)