This looks to me like a "cold shut", which is a type of casting defect.

"Cold shuts occur when two relatively cold streams of molten metal from different gates meet and do not fuse together properly during the casting process. This problem is visible to the naked eye – giving the appearance of a crack separating the two sections."

https://www.haworthcastings.co.uk/news/the-differences-betwe...

Cracks caused by impact have sharp edges and cracks caused by cold shuts have more rounded or sandy looking edges.