Thermal energy is not the same as heat. Heat is energy transferred between substances or systems due to a temperature difference between them. So it is correct to say that a system contains thermal energy, but not that it "contains" heat, since heat means energy that is transferred from one thing to another.The amount of heat transferred by a substance depends on the speed and number of atoms or molecules in motion. The faster the atoms or molecules move, the higher the temperature, and the more atoms or molecules that are in motion, the greater the quantity of heat they transfer.
