The fact that you are upset that they supplied the restaurant owner to field your complaint, and not a piece of stiff paper, shows you know little about giving feedback. Who better than the owner to hear your complaint?

You wanted to give feedback and they gave you that opportunity. It didn't have to be a confrontation - all you had to do is say exactly what happened. And justify to the owner's face your outrage that you received a yam instead of a sweet potato. Perhaps that was hard to do.

I ask for managers all the time. They often sit at the table with me and listen to my feedback. When justified they make an adjustment or give me a dessert, etc. They shake my hand when leaving the table. Hardly confrontational.