It has much more to do with how GPS receivers calculate a horizontal position when they have limited satellites in view.
I don't understand the math but essentially you are trying to solve four unknowns. Latitude, longitude, elevation, and the time offset between the satellite and device clocks. If only three satellites are in view the only way to solve latitude and longitude is to assume a value for elevation based on previous results. Without a forth satellite the GPS simply doesn't know what the altitude is. But that estimated value is sufficient to give a good estimate of horizontal position.
I don't understand the math but essentially you are trying to solve four unknowns. Latitude, longitude, elevation, and the time offset between the satellite and device clocks. If only three satellites are in view the only way to solve latitude and longitude is to assume a value for elevation based on previous results. Without a forth satellite the GPS simply doesn't know what the altitude is. But that estimated value is sufficient to give a good estimate of horizontal position.