When recipes are available on the internet, they are usually placed by the author or with the permission of the author. It's standard practice to allow small selections of a book (of any kind) to be published -- anywhere -- as part of an article or review. It helps to promote the book, which is a good thing. I doubt that the author whose work you saw was paid. Whether she was even asked depends on the site. Some people think they are doing the world a service by sharing -- without permission -- another person's good work. As a writer, and the wife of a writer and former book publisher, I can say with some authority that people tend to think that writers don't really work. But as you and I and every other writer (of recipes, poetry, novels, or appliance manuals) know, it's always work and isn't always employment. Writers have a hard enough time eking out a living without their work being handed out for free without their permission.
The question of what makes a recipe "new" or the "property" of someone is really the matter of a different ethical debate. Recipe writers tend to be resigned to having their work cribbed, adapted, or claimed by others. The main way a recipe becomes lost in the vortex is from being passed from one person to another like a game of Telephone. I have plenty of hand-written recipes in my files labeled "from Vasilka" or "Betsy's Wedding Cookies." When recipes are passed between friends, sometimes they are copied verbatim and sometimes they have changes made by the person handing them out. I, and most food writers I am sure, try to trace them to the source and give as much of an acknowlegment as possible. It's why I like to tell stories about where my recipes have come from.
Sometimes people are too modest about the changes they have made to a recipe. One recipe in my book (for Tomato Crostini) came from my husband's aunt, who went to great lengths to explain it wasn't her recipe in spite of the numerous changes she had made to it. Her version was so different (and better) than the original she described, there was no question that hers was merely inspired by the original.