Back on December 5, Lynne Murphy reported in Facebook about an essay-marking game — drinking a shot of liquor or eating something whenever a particular expression occurred in a student essay:
‘concordance’ to mean ‘example found in a corpus’, as in ‘COCA has three concordances of this collocation’.
… I’ve read this so many times, that I actually looked it up to see if this terminology was polysemous in ways I had not yet appreciated.
(No evidence for it I could find in dictionaries.)
So an error, but what kind? Mishearing (of occurrences)? Classical malapropism (perhaps as a result of learning the technical term concordance)? Eggcorn? Examples like this can be remarkably hard to classify.