Likely, but it seems they aren’t 100% sure of that at the Encyclopædia Brittanica. https://www.britannica.com/list/7-surprising-uses-for-mummie...:

“It was claimed by author Mark Twain that mummies had been used as fuel for locomotives. In his 1869 travel book called The Innocents Abroad, Twain describes the first railroad in Egypt. Because of the lack of trees and the price of coal, Twain claims that the Egyptians used mummies instead. He wrote, “[The fuel used] for the locomotive is composed of mummies three thousand years old, purchased by the ton or by the graveyard for that purpose.””

Also, FTA: “we know the British imported mummies and bones from Egypt on an industrial scale”