Once the core of the fire is mostly charcoal temperatures can climb up to 1100C. It doesn't have to be windy or even a large fire. Just need to be burning charcoal and not evaporating water or burning off volatiles.

The fires I have found aluminum globs in were long burning beach campfires and a bonfire to burn brush(big fire). The beach campfires were moderately sized but they certainly weren't bonfires built with 6-8 foot logs.