I've put the wrong oil in an engine before. It was on board the transport aircraft I was downroute with, and since engines isn't my main trade - just did the week on topping up oil, emtying the crappers etc - I assumed the oil on board was the oil to use. It was in an identical shaped tin, painted green, with white writing on - just like the can I should have used (only a different OX number)
No serious harm done, just an engine which had to be drained and refilled several days later when someone spotted the wrong oil on board and I got quizzed / bollocked about it.
Of course, I'm older and wiser now, and have learned not to trust anything I'm not familiar with. Never assume...