This was my old sifu's assertion. Beyond that, he held that even Cantonese was often inadequate to convey the proper use and feel of a technique. That is why Wing Chun is passed down through the hands. Not through books, posters, videos or even the ancient kuen kuit.
Of course, of course, all the above can be helpful in a supplementary way ... but they are not sufficient by themselves. This is why he (and most other old-school Chinese instructors) always tagged the forms and sequences featured in his books, videos, and posters with a few deliberate errors as "tells" to expose those who had not learned from a legitimate source.
As a educator by profession, that is something I found ethically troubling. But it was the custom.