Necessary? If you've heard a word used in a particular context/usage it's fine to say this is how you've heard it, also fine if you say someone else has described it thusly.
Telling someone who speaks a particular language, which you don't, that you understand the general usage of a term better than they sounds a little like hubris; the point Chris made was that he is familiar with the term in martial contexts as well.
I don't believe he mentioned shopkeepers at all and, even if he had, why couldn't a shopkeeper also have martially relevant knowledge?
That's pretty much how he operates. His understanding of something is never wrong, you just don't get it the way he does.