Consider the following symbol:
Does this symbol represent a pie from which one piece has been eaten? Or does it represent the last piece of pie? Or does it represent 10:00? Or how about a geometry problem concerning segments? Planetary motion? A teepee? What does it represent?
Let's say that the only information you have to go on are the physical properties of the symbol. It's height and width, circumference, segment lengths. It's color wavelength, and the charge, spin, and mass of the particles that it consists of. The only information you have is physical information. But none of this information tells you what the symbol represents.
This holds true for computers as well. If we find an alien computer, we can't assume that the electrons pulsing through it's circuits represent "1" and that the lack of a pulse represents "0". Perhaps the opposite is true. Or perhaps they are using something other than binary, such as base 12, and an electron pulse means "12", the lack of a pulse means "0", two pulses together means "1" and so on. The point is, from the physical properties alone, it is indeterminate what these symbols represent.
But if one is a materialist, then all that exists are physical properties, and hence nothing has any determinate meaning, including thoughts. And hence, the thought "materialism is true" might just as well be the thought that "there is no God but Allah and Mohammed is His prophet". As with the symbol above, neither meaning is "more correct" than the other!