One thing I find strange (assuming accurate analysis can be made on food that has been cooked, as the link gav posted seems to indicate) is how would the chef test the food to be sure it wasn't an absolute disaster/obvious it wasn't the meat the customer asked for?
"Oh, hang on, let me put my best french chef apron and test the meat for right levels of seasoning and tenderness"
In order for the customers not to be suspicious about which meat they are eating, I would assume there would need to be some test a-priori by the chef to be sure the meat was viable as a replacement, in terms of flavor and texture (essentially the latter, seeing as a piece of stock or prior marinating can change the former massively) and in fairness, I see this more of a practice of the chinese than the bengali/pakistani/indians.