Unlikely that it was actually salted bacon grease. More likely they applied an automotive grease and just jokingly told you it was bacon grease.
You could always test modern salted bacon grease an a piece of cleaned steel like some big common nails in board, bacon grease them and set them aside for weekly observation.
Same for brake fluid oil, the type that warns not the label that this product can absorb water vapour from the air.
Wipe some of that oil on steel and see how long it takes to rust.