I think keeping the minnows is a fine idea. I've done it many times over my life. Often bait shops stock local minnows and they can be extremely hardy. Depending on the type they might outlast anything else you have and will likely quickly take to flakes or other processed food, unlike a lot of wild fish.
I have no interest in tropical fish or other store pets and have always kept natural displays in my room at home. That also means I have broken a lot of laws but so be it. Most of them were rescue cases, in a drying up creek or other doomed situation. I'm glad I didn't let a broad sweeping law designed with objectives in mind stop me from doing a good thing. I'm surprised to see other fishkeepers on your case about this, as I think we would all be in agreement that keeping the minnows is better than pouring the lot of them out on the ground to perish.
Never release animals in a non-native environment, but it doesn't sound like your friend has brought baitfish from across the country nor does it sound like he's releasing them. Laws are indeed in place for a purpose... do these laws apply to you and what you are doing? If not then it's a trivial matter and I hope it won't stand in your way of appreciating the life around you.
I appreciate your friend wanting to keep non-petstore animals and hopefully he will gain a greater appreciation and knowledge of his native wildlife, as have I over my life. Best of luck, I think he will be quite successful.