It looked to Me like the wedge holding the king pin in had dropped out, this to My knowledge has happened in the past with both a Burrell road loco and also a McLaren.

The video suggests the engine lifted enough for the pin to disengage with the axle allowing it with wheels to run back under the engine i.e. no collar /bolt or whatever at the bottom of the pin. .

They are certainly more likely causes, so how did the broken casting story start?
Martin

from memory, pictures put on facebook by the owner.

Sorry no links from me 🤪