Yes it is as you describe.
I assumed just proving some infra red would trigger it, maybe it needs to 'see' motion.
Might try that with a couple of leds.
Edit: Just read on on Pir motion sensors, apparently theres 2 sensors, 1 'watching', and 1 blind, the blind sensor picks up the overall temperature and its used as a reference for the 'watching' sensor to prevent false triggering from temp changes, also some have some kind of filter to remove signals from large flashes of light such as from car headlights, so maybe the way to trigger one is to provide a slow changing amount infra red, and not so bright, so as to mimic what the sensor would 'see' if a person or critter walked past.