Factual error: SS officers did not carry a unit identification tattoo on the forearm, as implied in this episode. Most (but not all) carried a small, black, blood group tattoo under the armpit.
Factual error: Sunflowers are not grown in the North of France. They're grown primarily in Provence and Poitou.
Answer: They are using the accepted names of the bombs. During World War 2 the Germans used the metric system and produced bombs ranging from 50kg to 2500kg. Referring to the weight of the bombs in pounds (or fractions of tons) risked confusing the situation and would require someone to understand how to convert from imperial measures to metric, not an easy thing to do when under stress.