[and the timing chain the *person* put the master link on backwards I dont know how but I saw it myself and couldnt believe it
1982 380 SEC]
The chain link thing is a bit of an oddball from motorcycles - yes, I use them also!.
In theory, if the split link end is pointing in the direction of travel, a stone jumping up from the road could open the link and thus allow the chain to seperate. You can figure out yourself the chances of this happening in a sealed environment like a timing case.
However, some dumb mechanics continue to preach it as gospel without thinking the thing through. I suppose it gives them a chance to show how smart they are...not.