In Celcius, it's less common to round to the nearest 10 degrees (or say things like "in the twenties" as you might with Fahrenheit), because that makes a much larger difference than it does in Fahrenheit. So I wouldn't necessarily assume that "20 degrees" only has one significant digit unless it's explicitly stated. (I haven't checked the original paper, though.)

However, converting something like 21°C to 69.8°F is indeed silly and should just be 70°F.