i suspect its mutton ie older lamb, that is used when discribing a meat curry. This meat is far cheaper than lamb, chewier, stringy and most likely needs some delicate preparing anf cooking to make it palatable.
from wiki
* Lamb ? a young sheep under 12 months of age which does not have any permanent incisor teeth in wear
* Hogget ? a young male sheep or maiden ewe having no more than two permanent incisors in wear
* Mutton ? a female (ewe) or castrated male (wether) sheep having more than two permanent incisors in wear
i lay money on it that meat is mutton, in scotland this is often the case though usually its minced mutton ie meat pie, more commonly known as a scotch pie.
nothing wrong with mutton, as long as you understand its a cheap cut, then you probably get a bit extra compared to lamb in a bir.
i guess just ask them next time you go to a bir
put mutton curry into google images and you will see many lovley curries.