One of my pet peeves is being "shushed," for whatever reason. I think the teacher was out of line to do so. If the owner doesn't want her
discussing stuff they can't sell there, that is fine. But I think it would be in extremely poor taste to insist that customers bring OR discuss only supplies from the shop. That's just silly.
I bet the teacher has been reprimanded for discussing things they do not sell and thought she was "saving" you from getting a remark from the owner. In fact, the owner probably would not have said anything (at least I would hope that is the case).
Some LYS owners are
a little weird, though. I encountered one shopper at a LYS who had been trying to get some specific yarn for a specific pattern, and had been turned down to purchase it at another LYS. The owner had
the necessary yarn in stock, but apparently thought the project was beyond the knitter's abilities. She actually refused to sell it!
I was floored. But apparently this particular store owner has a rep for being weird like that. (Like it's her stash, not a store,
People continually surprise me.
So yeah, I wouldn't ban myself from the store, but I would be a little irked. Actually, I probably would have said something like, "Oh since you don't sell these I'm not allowed to talk about them, is that what you're saying?" really loud.