It's just someone playing around with their SSID name. And EXT would probably indicate it's their guest network.

the _ext usually indicates a range extender...

Someone else called their router that. Lots of jokers will give their name things like that.

Some router owner named the wireless network that is all. It's same deal as the ones that name their network 'FBI Surveillance Van'. Clever, but probably makes them a target for hackers first.

No FBI_Surveillance_Van?

Is there a van outside that says "Two Guys from Quantico Pizza"?

Change it to "Trump Won"

I like mine

THEDONALD.WIN4NEWS

People having fun when they name their routers. You can name it anything you want. Laughing at some examples on the web.

Ext is often a repeater device.

I made one named NSA_Listening_Post back when I lived in-town. Got lots of giggles off of it.