First of all, why are you blindly believing the assumption that the flash was caused by a boulder striking the moon? That IS merely an assumption, a theoretical explanation as no one actually saw a boulder in flight, only the flash, and it was immediately assumed that 'something hit the moon'.

My theory is that there is some strange happenings on the moon, although I'm not sure what, and that this 'flash' or quite likely explosion is related. My search to uncover this had led me here.