Each farm in Norway had a name. The farms were not like here. There would be several different households on one farm there which would have a name. Each household/farm/bruk would have a number or the plasses would have a name as well. So Gonstad was probably the last farm they lived on when they were in Norway and that is why they chose it. Some farms would be like Upper Gonstad, Lower Gonstad, etc.
In Norway, back then, they did NOT have surnames. They had their given name and then their father's name with a son or dotter after it and the farm name was also given like and address. So Ragnild would have been Ragnild Halvorsdtr (Halvor's dotter) (in US Halvorson) Gonstand. If she moved to another farm, that farm name would be used. The naming conventions can be confusing and once they came to the US, they would use whatever they chose. It was much different back then.
It is quite complicated at first. You'll get the hang of it. The farm would get it's name from different things, but sometimes from a person, not often though. Say for instance, Lund which was how the thread started on the other board. Lund is a farm name which means grove so there was likely a group of trees right there. Lund is common in Norway, Denmark, Sweden and even in England or other places where the name was taken.
In the earlier years there were a few family who actually had surnames but generally they were nobility or families from other countries - you'll see it, the more research you do.