To make matters worse, I have REAL doubts that this headlamp can live up to its claims. Although I can't say for sure, it looks like it has a 5mm LED. You will NEVER get 200 lumens from a 5mm LED.
There's an optic, which makes it hard to tell, but it seems unlikely someone would claim 200lm from a 1x5mm light.
At least, outside certain online marketplaces.
And a 1x5mm light that had a 8hour runtime on 2xAA would have either a woefully inefficient driver or would burn the LED out in no time
The fact that it doesn't list a specific emitter (which most any manufacturer is proud to do) doesn't look good in this regard. Also, a runtime of 8hr at 200 lumens on 2xAA? Not happening.
You're dead right that regulated 200lm for 8 hrs on 2xAA is bollocks, since it would require about 10Wh from 2xAA, which isn't going to happen, but even the 'ANSI standards' were seemingly designed by manufacturers expressly to allow unregulated lights to make seriously misleading claims.
Like any other light, if it produces 200lm after a few minutes it can then drop horrendously and still meet the ANSI standards, let alone even worse ones.