There is nothing wrong with Walmart hunting clothes and gear although it would be on the lower end. I suspect that your instructor, might have a hidden agenda
I've been a hunter safety instructor since 1986. Let me try to explain this from an instructors perspective and tell how I cover this in my classes. As part of the class we are required to do a section on survival, which was one of the sections I always taught.
If you are on a casual hunt on the family farm and never out of sight of a road, or other structure most anything will do. But if you ever hunt in a wilderness setting your clothing selection can get you killed. Walmart sells nothing I'd use on that type of hunt and it has nothing to do with making a fashion statement. For that matter Bass Pro shops sells nothing I'd hunt with, including boots. Cabelas has a few items.
There is a well known phrase in wilderness settings. "Cotton Kills". Never wear ANYTHING made of cotton in the back country. You might only be uncomfortable in summer, but could die the rest of the year. Wool,or quality synthetics is the only way to go. Good boots that won't let you down are vital. I'm aways looking at a bargain, and have 2-3 pairs of boots that retail at $300+. Fortunately I've always been able to find something heavily discounted and have never paid that much. But I'd not bat an eye to pay that much if I could not find a bargain.
The more rugged and remote the hunt, the more important quality clothes become. I've been on solo backpack hunts in areas so remote that if I had fallen and broke a leg my body would likely never be found. Walmart clothes have their place and do fine for most situations. But as a hunter safety instructor we have to assume that some of our students may someday end up on a remote hunt in the middle of Alaska. It is our job to prepare them as well as we can in a short class.