Restaurants do a lot of things to attract their customers: colorful signs, fish tanks, sample dishes, discounts, menus, ... It is unusual to see a restaurant that makes no such effort to attract customers. In fact, there is no way for people on the street to find out what kind of food this restaurant serves, and what the prices are. They make no effort to bring you in. It seems they do not want your business.
This is, of course, a “canteen for tourist groups from mainland China”, 「內地團飯堂」, situated next to the wet market in To Kwa Wan (土瓜灣). This is a place frequented by working class locals, with few, if any, tourist attractions. I noticed this particular one several years ago. I was mildly surprised that it was still in business yesterday.
There is also this chocolate shop, across the street from the restaurant. It is next to a fruit vendor, directly under a old people's home, and directly facing a huge pile of used styrofoam boxes. Busloads of mainland tourists would be disgorged by buses, pile into the chocolate shop, walk across the street to the canteen, and get back on the bus now parked outside the canteen, without visiting anything that can remotely be considered "tourist attractions".
There is actually a temple at the street corner dedicated to "Tin Hau" (queen of heaven), a goddess worshipped especially (at least originally) by fishermen. It is frequented by locals. But I have never seen any mainland tourists there.
It seems to be a characteristic of low-cost tours organized by Hong Kong and mainland China companies - “tourists” eating and shopping at specialty stores catering only for them, far away from the normal tourist attractions. One wonders whether this truly qualifies as “touring”.