Yup! Whoops! I was surprised by the brightness of the spark and thought, uh oh. It wasn't like spark plug bright at all but having never pulled that wire before either I don't know what it may have affected.
The alternator field is an electro-magnet with a large amount of inductance. If the field current is broken, the energy stored in the inductor is released, it goes to high voltage in attempt to keep the current flowing. The voltage can easily reach hundreds of volts, resulting in the spark. Ignition coils work in a similar fashion, but also have secondary windings, that transform the voltage to an even greater value. Yes it can damage other electronic devices, but that depends on the source impedance of the wiring back to battery. The higher the source impedance, the more voltage is induced in the IGN circuit.