I guess everyone that has ever made it didn't know what they were doing then.
Then the day old bread is dropped in a low, flat dish, turned from one side to the other quickly enough not to soak up too much liquid, then placed in a hot skillet (with either butter or oil heated in it) and fried to golden brown on first one side then the other.
I usually add a bit of cinnamon and occasionally a teaspoon of sugar in the egg/milk mixture, especially if I'm serving the "French Toast" as other than breakfast, and dust with powdered sugar.
My French Toast recipe starts with an egg; the reason it’s called French Toast is because there is an egg involved. Ever wondered about French Vanilla ice cream? Same reason. French Fries might be the exception, however in the 60’s some places made ‘fries’ out of mashed potatoes mixed with eggs then pressed into hot oil with special tubes somewhat like a spritz cookie gun. I don’t know when the whole ‘egg in something makes it French’ got started, but there are a bunch of food things called French only because they have eggs in it. Same with wine. Coq au Vin springs instantly to mind. A tasty dish from the 50’s given a ‘French’ name to make it sound classier.