I'm not an expert on it, but that sounds a bit like Mangalorean-style, which omits tomatoes and includes tamarind... weird thing would be that geographically, that hails from southern India, rather than the north (which is what Nepali cuisine is usually more akin to).

Was this at Royal Nepal, by chance? I've had their Vienna location's food several times and enjoy it. The Vienna location kept more of the prior restaurant's menu (Momo House, also Nepali, but which went under about halfway through the pandemic), which includes some tasty street food items not on the Alexandria menu but lacks the yak dishes you can get in Alexandria. I haven't tried the chicken as I'm usually there with vegetarian friends, but the menu describes it as "Rich Creamy Cashew, Tomato Gravy Dry Fenugreek, Clarified butter," and the photo certainly looks a lot darker than the typical butter chicken at any of the area's Indian restaurants.