Just looking TKS
It is impossible to see into the exhaust of CF6 engine from the ground without having a ladder of some sort. Also it is extremely difficult to see anything put in the front of the fan and resting at the bottom of the intake. During the day time perhaps but night time very very hard.
I would be more inclined to ask the question as to the use of a wheel chock in the first place? An approved tool for the task that was performed? How does a wheel chock fit in the tool count? Remember all tools should be counted when starting to perform maintenance and then counted again to make sure that no equipment is left in the aircraft causing such incidents.
Apparently it was the Ice-engineers assistant who left the chock in the engine and the failure of the engineer to make sure that all work was properly completed and all tools accounted for.