Ah, I see. Wouldn't say that coastal indian cuisine doesn't use yogurt at all, but he has a point. But (preferable full-fat, and real, indian 'dahi' will contain even a lot more fat) yogurt will most likely not curdle if used correctly ,) Cream is a pretty good guess! Maybe even some coconut cream?
But, and DalPuris suggestion is pretty good, did you already ask which part of the world these dishes come from? Could be some Sri Lankan curries after all ;D But I'd still go with indian ;P
I'd guess the okra dish (recipe page one) lacked some flavour. No chili at all? Maybe a pinch of cumin and/or coriander? If we are talking about south indian cuisine, you could try to throw in a few split urid beans and roast them, and keep them in there for taste and texture. Or using a masala paste. But you know best how it tasted (:
Could it be, but I doubt it somehow, that they make their own coconut milk? If so, they have total control over the consistency. Just some ideas (: