In other words, some of the basic principles and ideas of advertising, of marketing, came from people working in the patent medicine industry, in the patent medicine business.
When we're talking about physical things, then we use the word " patent." Patent medicine, however, isn't patented medicine, so it's something of what we would call a misnomer.
Patent medicines are medicines that are sold and advertised as being cures, as being something that will solve a medical problem, but typically do not.