This was a partial mash, which would explain your weird readings I think. You half mashed and then added water and extract. Supposedly boiling for 45 min would mix everything, but then again, I've seen crazier things. Based on the recipe you posted, I would say a 1.020 would be impossible.
You missed my post about the 1.020-1.030 being a huge range apparently . That is literally almost a percent of alcohol depending on the beer. No worries. Live and learn, and MAKE MORE BEER!!