The silverware is magnetized because it is not silver! Silver itself is diamagnetic, which roughly means that no matter how strong of a magnetic field you expose it to, it will not respond to that magnetic field. (that's not 100% accurate, but without a really detailed discussion of magnetism, it will do for now). If the flatware is magnetic, it because there is likely some material underneath it that is ferromagnetic, like iron or nickel or cobalt (or an alloy that is ferromagnetic). Ferromagnetic materials are inherently magnetic, which means that they naturally become magnetized by sitting around in a normal environment. They can only be demagnetized by undertaking great efforts to do so. The flatware you're using is probably an iron/steel alloy that might be coated by silver.