Really, you have no grounds for complaint. The bloke was carrying out his job which authorises him to inspect aircraft in an aviation environment where the aircraft can be put into the air at any time.
It's no different to you driving your car on a public road and being pulled up and stickered by the cops for a mechanical fault. By driving on a public road, you are essentially putting yourself under the authority and discretion of traffic police
You are talking about two different things here.
The scenario quoted is akin to the police turning up to your house whilst you are away entering without a warrant and defecting your car whilst it sits in the garage then as a result impounding your car.
That is very different from being pulled over on the side of the road whilst out driving.
Same with CASA. The question being raised here is does CASA have the right to enter a locked hangar and search and defect aircraft whilst in there?
I would highly doubt it.
You could for example realise that the aircraft is defective so therefore leave it in the hangar whilst waiting for parts (and/or sticker in this case)
If you had a private airport for example there is no way they could enter and search without going to a judge and showing reasonable cause.
So for CASA to start entering and searching without a court order anywhere is a very big call on their behalf.