I am not sure about Lee Chin Eng's use of sunlight. It may not have been universal. In my very old copy ((C) 1967) of
Salt-Water Aquarium Fish by Axelrod and Vorderwinkler, there are several pictures of aquariums set up by Lee Chin Eng. Some do not have an obvious source of sunlight, and the whole tank pictures show a more or less conventional reflector strip.
I'm also not sure about the corals involved. Looking at the old photos, I can not find any obvious live corals. I'm not saying that there were none in the tank, just that I couldn't see any. Then may have been small. The live rock looks like cured base rock, with some live on it. In some pictures the rock looks overgrown with algae. I will admit it's tough to tell because the pictures of that day tried to show off the fish rather than the invert live.
To quote from the book -
"Lee Chin Eng took pieces of living coral, complete with all the assorted life to be found along with it, and put it into the giant marine aquariums that he maintained in Djakarta. He took away all his filters and just had a small airstone with a few bubbles to give some slight movement to the water to better simulate nature. In a few days the coral 'came to life' with small anemones blossoming out, featherwoms, small crabs and other crustacea darting forth, and small polyps making their amazing appearance. For months the coral grew and more and more life was evident. As the coral grew, so did the fishes. ..."
In the 352 page book, only about one page of text is devoted to the natural aquarium method, and little specific information is given. The description sounds more like a description of live rock rather than coral. I would suspect that if there were corals here they would be small colonies on the base rock. There may have also been recordia, zoos or similar anemones on the rock. This would have looked like "live coral" in 1967. We would not expet to find a lot of other live creatures on a coral today. Also, the lighting systems of the day would be unable to support most of the corals we take for granted today. Most fixtures had only a single normal output "grow lux" flourescent bulb, or several 25w to 40w long incandescent bulbs. Of course if lots of sunlight were available, that could make the difference.