ADHD gets referenced here frequently as a result of too much screentime/social media etc. However, the hypermobility and ADHD association is pretty well documented. While it's true that people may start to show ADHD like symptoms as a result of the internet etc., no one spontaneously becomes double-jointed because they're distracted by their phones.
Anecdotally, my sister and I are both ADHDers with significant hypermobility. My mom has a double jointed thumb but no ADHD, and my dad has (undiagnosed but likely) ADHD but no double joints.