I don't wish this to be an argument, just a statement of fact.
When I began photography near the beginning of WWII, 4x5 was considered medium format. At that time there were still folding roll film and box cameras which produced this size negative.
The discussion in those days was whether 5x7 was medium or large format. 8X10 and larger was considered large format.
I don't know when the movement to call smaller formats large took place as I never worried about such nomenclature. I suspect it happend in the 50's when the number of sizes of roll films began to lessen, and SLR's like the RB and Rollei SL66 came on the scene.