Those are decent rods and great fasteners. Its got to be a rod bearing/spun failure as you have surmised.

I think the bearings weak link is the OE little tabs that secure them in. I think they should all be pinned in. As is when they see a little extra friction from lack of oil and they spin.

If they stade in place we would just see some bearing damage and not broken rods and blocks and everything else that can occur.