Are "store brand" foods made by popular companies?!

That is true for most things since Store brands (or house brands) are often made on the same facility. The main difference is ratio of seasonings... Kraft has their proprietary blend while a store brand would just use a general blend.

Yes, most of them are made by Name brand companies, you can read the generic brand's label to find out what major company makes a generic brand. The product is not the same, it usually tastes different but it doesn't mean it's inferior or not good for you. Store brand food is a good alternative if you want to save a few dollars.

en.wikipedia.org

In most cases they are by the same companies and are exactly the same.