and wrong part IMHO.. but not defective..
he grounded the base of the solenoid then hit S with power.. solenoid engaged. that's wrong part.. not an iso base. my guess is it's a bypass solenoid
he then added a ground to I and hit S with power and solenoid chattered.
when solenoid pulled in with S being powered.. then there was a ground present common to battery, menaing ground present common to that jumper to S.. and that probably kicked her out.. which broke ground path and let her pull back in.
sounds like a ignition bypass solenoid to me..