When the PNP turns on, the 10uF cap is charged thru the base-emitter junction of the NPN. The charging current of the 10uF turns the NPN on hard but when the 10uF is charged, the current thru the 330K resistor is not enuf the keep the PNP saturated. Now, since the 10uF is charged negative at the NPN base, it starts discharging thru the 330K resistor and the base of the NPN is driven negative. Since it takes longer for the 10uF to discharge than to charge, the duty cycle (on time) of the LED is small and the average current does not exceed the 20mA rating of the LED even tho the peak current is 165mA.