I'm not saying that you're dad got it wrong at all, but times must have changed. I'm living in NZ at the moment, and after I started reading all the info on here about grass fed vs grain fed etc. I asked at a couple of butchers about their beef, and each time I asked if it was grass fed I was looked at like a lunatic "what else would they eat?" was the usual response. This country is essentially one huge field / paddock where cattle and sheep graze on grass to their hearts content on lush green grass. So, yup beef served in fast food restaurants (if it is just beef..) here is very likely to be grass fed.
In fact, I've had very little success in finding any mention of grain or corn fed beef being sold here, or even mentioning it, apart from a few locally published articles which seem to be regurgitated american articles and one restaurant which actually advertises a grain fed burger as a specialty
According to the beef NZ website NZ "Beef cattle production systems are pasture based" which could also be why "The majority of beef produced is exported" and "North America dominates beef exports, most exported beef is destined for the processing industry".
I've driven all over this beautiful country and have certainly not come across any feedlot farms, but have seen big healthy looking cattle roaming all over the place