It’s not plugged in. It’s leaning on the Aerial socket. You’re looking at the bottom of the emonTx pcb, and the bottom of the ESP module. So GND is on the left in both cases, even though it’s off the picture for the emonTx.
So in Colin’s photo, the pin that IS connected (4th from the left) goes across to the 5th from the left, which is the one labelled “Rx” on the emonTx but is the one it sends on.
(If you remember the very first information published about the ESP, the photo showed the Tx & Rx pins twisted around each other (but not touching) to make the crossover Tx→Rx & Rx→Tx (in real terms - not labelled pins 
)
This I think is a later picture: Using the EmonTx v3 with the ESP8266 Huzzah WIFI module
Colin’s appears to be OK, even if the emonTx has the later software that does accept serial input.