He does indeed mean a 15 or 20 seater. You'll be driving those depending on who you work for.
Dangerous good certificate is a must.
First Aid certificate is a very good idea.
Work is seasonal, predominantly during the Dry season aka Winter. However, most go up during the Wet to get established.
Spend some time researching the area before you go so you have half an idea as to what to expect lifestyle and job wise.