It depends on what you call a 'farming society'. If it's about where their priorities lies, Vikings are not a farming society. They valued fertile lands and resources, and expanded where farming would be better, but that doesn't make them primary farmers until they fully settle and stop invading neighbors.

The same way I do chores, but I'm not a house maid (until perhaps I quit my job)

As far as I know, Scandinavia was absolutely a farming society to the same extent England and France were. It's not like they all up and went a-viking: the people that did were a small percentage of the population, and this is to be viewed as equivalent as Rome sending the army (a small percentage of Rome's population) to conquer Gaul. They aren't suddenly considered less of a farming society when they do this. It's just how farming societies fight each other.

This form of selection bias is extremely common. An ethnic group and their neighbors rarely meet, if they do, then one side is a military force on an expedition which leads to a characterization of the ethnic group being violent.

Examples: Vikings, Barbarians, Huns, ...