Sounds like what we called "Bull Ants" as kids ( i grew up in Adelaide )
Also sounds like yr mate got stung, not bitten.
We always had fun with "new arrivals" to the area as we told em the only way not to get "bitten" was to grab the ants by the head.
They got "stung" instead :-) ( and that then normally got infected )
Spit and dirt. Worked with every ant bite/sting/invenomation I ever had and being part bush kid, that was offen! Green ants and bull ants. Doubt it would work on Fire ants but they are only a recent immigrant so thankfully haven't had to experiment.
Used to tow cars on the Mid Nth Coast NSW. Ants are particularly partial to Holden Commodore computers, especially when they're parked in the same spot in carports overnight. Saw this occur on several occasions..........
Anyway, it is the hum of the electricity that draws them in -right frequency, watch out.
Interesting theory, I get them in the some of the light switches at the shack. We have solar power so there is no 50 cycle magnetic field to attract them the majority of the time. There are however a couple of cycles of power every few seconds in standby mode (to allow compact flouros to start the inverter) enough kill an ant.
I wonder if the buildup occurs after death by misadventure, one ant strays in to the switch, gets zapped, then more come to the rescue and suffer a similar fate. This article seems to bear that theory out. https://www.livescience.com/37720-cr...ectronics.html
bugger the ants they are not getting it. 
huge a mate got bitten on the arm by one, made a mess and he was in agony
