Google does not have the authority to "send the police". They reported content that looked like CSAM and the police did what police do and assumed the guy was a criminal.

The problem is not that they reported it, the problem is that they had it in the first place.

Agreed, that's pretty fucked up.

However, on some level it's to be expected that 3rd parties may report you if they feel you are engaging illegal activities (especially on their premises).

While I don't support technological backdoors, there are legitimate for society to engage in surveillance. It's the responsibility of voters to make sure that this is done in a responsible and transparent manner.