Hey Barb, late to the party, but knowing your hub's ancestry...
it was probably because the meatloaf was loaded with extenders (oats, breadcrumbs, etc).
Those 19th century people were poor and to have a meatloaf was luxurious. They extended it with filler. The more filler, the looser the meatloaf, hence, fluffier.
My dear German Grandmother filled her meatloaves, in the old tradition, like Frikadellen, with big wads of bread and oats. Baked into unctuous caramelized wondrousness with baked macaroni and cheese. Grandma knew how to keep me happy whether she was scrimping or not. And when she made Frikadellen, she told us she was making her "Deluxe rich hamburgers" for us. We bought it up and ate them like we were dining at the Russian Tea Room on Filet Mignon.
I would trade one more my Grandmother's Frikadellen for all of the Russian Tea Room's fillets.