What does amber – green traffic light mean in South Korea?

I recently rented a car in Jeju, South Korea. While I managed to get used to most of the traffic rules there which are different from what I’m used to (such as right turn on a red light) I got really confused by some traffic lights. Several times I observed the following sequence:

Red > Green > Amber and Green > Green > Amber > Red

Now the bold part has me confused for two reasons:

  1. I’m used to Amber and Red together (before changing to red), but I’ve never seen Amber and Green together. I thought it could mean that it’s about to change to Red, but that’s obviously not what’s happening since it goes back to Green.
  2. I would think that Amber usually indicates a change of the signal, however here it went right back to Green.

So what does this mean?

My research turned up the following:

From: https://ko.wikipedia.org/wiki/%EB%8C%80%ED%95%9C%EB%AF%BC%EA%B5%AD%EC%9D%98_%EC%8B%A0%ED%98%B8%EB%93%B1

However, this is not exactly what was happening, in my experience I saw the same but without the green arrow. My best guess is that this happens when one of the other traffic lights on the intersection go through the above change and maybe the Amber light is to indicate this change to my traffic light so that I can be cautious about left-turning cars, but I couldn’t find anything about this.