The difference is that when you are outside in the sun, there is visible light too, which means your pupils are about 2mm.

When you are in a dark room, they can be up to 8-9mm. This means 15x more light allowed in.

I am not saying that the LED in the video will destroy your eyes, but I do wonder if the eye-pain induced by the iPhone X that I had the past year is because of that.