This is done to ensure water runs off the roof smoothly and to protect the decking from exposure to the elements.
Metal roof drip esge over or under felt.
When the drip edge is being installed along the rake edges it would be placed over the drip edge.
At the bottom of the roof the drip edge goes under the roofing felt.
If the drip edge is going on to the eaves of the roof you would position it under the felt paper.
At the side or gabels of a roof the drip edge goes over the roofing felt.
Water will pass right under that drip edge.
On the gable edges the felt paper goes under the overhanging drip edge metal.
I have no idea why ask this old house did the drip edge the way they did.
On the gutter eave edge the felt paper goes on top of the gutter apron drip edge metal.