That's my current hypothesis.

[Slowly, his attention drifts toward the sky.]

If we assume this impact was the impact of the shards falling, then it could be the original Moon Warp. Still, that leaves many gaps within the timeline. It may be a bit too presumptuous to try and place these memories relative to this impact, when all we know is what was scrawled into the tower and the few remnants in those books you gathered.