IIRC it wasn't the fridge, it was the gelatin.

They came up with a much cheaper way of making it, so for a while jelly was cheap and readily available but people still thought of it as fancy food.

The hot dogs in jello thing sounds like a bastardized version of some actual foods from way back. I know the dish as "sült", but I'm sure it exists in many forms. It's basically made by boiling bones (think the ones with all the nooks and crannies, like the skull) until all the meat and gelatin come out. Then cool until it solidifies.

I also choose to believe this