They were able to extract DNA from a single premolar tooth taken from the mandible. The tooth’s cementum and enamel were removed, the tooth was ground into powder, and the sample was zapped with UV radiation to ensure it wasn’t contaminated. To determine ancestry, the team compared the Well-man’s DNA to a database of more than 6,000 modern-day Norwegians.
I guess, but the again, pretty much any sentient creature could tell you that drinking the marshy water with dead stuff in it is a bad idea. That’s a pretty basic survival instinct that I think we had figured out well before we had modern science.