The angle is determined by the duration of a pulse that is applied to the control wire. This is a form of pulse-width modulation, however servo position is not defined by the PWM duty cycle (i.e., ON vs OFF time) but only by the duration of the pulse.
The Servo library generates pulses of the required duration during the specified interval. That has nothing to do with PWM as understood by the Arduino. The analogWrite() function that does PWM on the appropriate pins controls the duty cycle, so that over some undefined period of time, the ratio of on time to off time is the proportion that the user wants. This pin diddling will not control a servo worth a damn.