When a motor lets go because of a rod bolt failure, the bolt doesn't usually fail all at once. There's usually a nick or something where the failure starts, and then "beach marks" radiating from the nick. When the break gets far enough through the shaft of the bolt, the remainder of the bolt then lets go all at once. The break in this bolt shows a consistent texture across the whole shaft of the bolt. That indicates to me that the bolt broke all at once, which suggests that the cap failed first, then, when the cap was completely cracked, the bolt snapped.