I am still curious, two parallel LED with opposite polarity, both can light up.
It is from a powerbank circuit I just open to repair.
The LEDs are for indicator.

 

When the voltage from pin 3 is positive with respect to pin 1, the left LED lights.
When negative, the right LED lights.

 

How about both LEDs turn on? What the explanation

 

If you switch the LEDs on and off, fast enough......they both will appear to be on.

 

If you switch the LEDs on and off, fast enough......they both will appear to be on.

Yea I guess this. The IC some kind of black box that have nano second pulse...that can manage 2 opposite parallel LEDs which one or both on off or blinking.
Small IC ,,,

 

Any pulsing beyond a 100Hz or so is not perceptible to the human eye.