Have you ever eaten/seen horse meat? I was served some meat at a relatives house in New Mexico that they called beef but it didn’t look like any beef I have ever seen. I went to the meat market with the relative when he bought it. The meat was very very dark. I called it elk but it was even darker than elk. It tasted OK, a little strong as I recall.
Could have been elk. Venison is darker than beef.
Ostrich is a LOT like beef as well. Someone could eat that and not know it was not beef.