The voltages used in your iPad are not very high and besides its not wired in a way that can get a complete circuit.
'''Please don’t do this! It’s an example for reference!'''
If I only touch the live side of the power feed cord and I’m completely insulated from ground the circuit can’t complete so the power won’t flow. If holding that cord and I touch a neutral or ground wire or tie point I would get a very nasty zap!
Here, the iPad is not wired to a charger or have any other means to complete the pathway. While the case is metal it only has one side of the circuit, touching any part of the case or the display won’t complete the circuit to the apposing pole of the circuit.