Stealing or co-opting? [Is there a difference to the Taiwanese and the Chinese?]

Spent late Wednesday afternoon planning, shopping, and preparing for a special dinner [per my fourteen-year-old's request]—Thai Clam Pot—one of his favorite comfort foods.  This recipe comes from one of my many beloved cookbooks lining one shelf of the pantry in our kitchen.  My son, however, insists that my spouse told him this recipe belongs to his nai nai [maternal grandmother], who then taught my spouse how to cook this dish.  [After showing my fourteen-year-old the recipe in the cookbook, his only question was "Why would Dad lie about this?"  Why, indeed?  The moment may have sounded sad but we capitalized on a great learning opportunity to talk about lying and the psychology of liars that ended with much laughter.] 

Should I be surprised at such blatant [and easily disprovable] lies?  Just this fact convinces me that habitual lying must be one among many "vise" in my spouse's "survival toolkit." 

What bothers me more about this discovery is the lingering question of how many other "innovations" and inventions—recipes,  programming codes, dance choreography, published research—that are claimed by my spouse and my mother-in-law as their own are, in actuality, handiwork of other people?