How much oil?
Exactly what was the mode of failure?
Without doing a failure analysis to root cause of the actual failed part(s) it’s impossible to say.
I’d have to suggest that it stretches my imagination to envision someone accidently adding oil to a master cylinder reservoir rather than the engine. They’re totally different looking, in entirely different locations, attached to different assemblys, and clearly marked. Anything is possible, and I’m not going to second guess the guy that did the work, but this one seems a stretch.