I guess this may be a weird use of word “pull-up”. On the same page they also drawn LEDs conducting from negative to positive (circled in the attachment).
Normally I would say to just grab a multimeter and measure, but it seems that pins 2 and 4 are both actively driven. That is to support two-color LEDs. So I suppose measuring resistance from pin 2 to +5V is not going to help. This is probably a driver circuit with output resistance equivalent to about 300 Ω.
If you are worried about destroying something, just put a 1 kΩ resistor between 2 and 4, turn it on and measure voltage across that resistor. It should read about 1000/1300 · 5V ≈ 770 mV when the thing is powered on and going up and down while in stand by. However, if it doesn’t it may still be because the driver continuously flips polarities to accomodate both LEDs. In such case I would go for a simple circuit with two LEDs at opposing polarities and something like 560 Ω resistor. They will be pretty dim, but enough to tell if the driver works as expected.