What gas are the bubbles that evolve in the redox reaction of copper(II) chloride and aluminum?
The gas bubbles are very likely just air that was dissolved in the water previously and now gets released. I would expect most of the bubbles to actually be nitrogen, followed by oxygen, argon and then some carbon dioxide — that is assuming you used deionised water which should not have significant amounts of carbonate and hydrogencarbonate dissolved.

The copper particles merely supply suitable nucleation sites for the gas.

The theory on aluminium oxide being oxidised to pure oxygen is not correct. Oxygen is a very oxidative element meaning that you require strong oxidants to oxidise oxide anions back to oxygen. With ‘strong’, we’re talking the oxidative strength of potassium permanganate. Aluminium’s oxidative powers are nowhere near that strong.

Copper(II) chloride and aluminium oxide do not react with each other; only metallic aluminium beneath the passivisation layer is able to react with copper(II) ions.