Did I damage ignition switch, could it already have been bad, how to avoid in future?

I recently asked Is my ignition switch cleaning ok? and answers said the switch is probably faulty as copper has been revealed.

My question is did I do this, could it have been avoided or was it already like this or inevitable? You can see a before and after of the cleaning in below pics.

Did I do something wrong like sAnd too aggressively or could this have been cleaned/avoided by lighter sanding? Was sanding even required/might tissue have done it? On the other hand could the black stuff have become so attached to the plate that removing it would have caused the silver layer To come off anyway?

Thanks