You have connected +ve of all LEDs to 3.3V and each negative pin to IC pins. So when ever an IC pin becomes LOW (means it internally connect to ground), that particular LED light up. If the IC cannot source current, (ie it can only sink current), then the only way to glow an LED using that IC (i/o pin) is by connecting the -ve of LED to IC pin and +ve to supply voltage.
But be careful, if the internal resistance of IC is very low, it can damage the LED because for a normal LED, 3.3V can damage it easily. Use a resistor, say 100 ohm in series with each LED. U can design the resistor value by considering a maximuim current of around 10mA through an LED.