It's not mind reading. They have a quantum computer that simultaneously tracks your actions in infinite universes. In an infinite subset of the infinite universes, you didn't just think of buying a USB-C card, you actually searched for one. In a smaller infinite subset of the infinite universes you didn't. And in another infinite subset of infinite universes you watched some fat chick ride a dragon dildo. So, they collapsed the wave-function and determined that in this universe you are most likely thinking about buying a USB-C card. But don't worry, they'll slip the dragon dildo into your feed soon enough.