This is quite a dishonest interpretation of the facts. They were arrested because they participated to an unregistered (therefore forbidden) protest, there was proper communication from the police that such event was not authorized because of the expected violence issues, and the goggles / masks were proof of participation.
It's pretty easy to start a protest rally or march in france, you just have to declare it to the prefecture. Sometimes they are not accepted, for instance when a protest with violence history wants to pass in certain parts of the city with a lot of shop (they are regularly attacked). It happens that violent protestors such as the yellow vest types declare a march passing for instance the Champs Elysee avanue (famous locally for its numerous shops), knowing it will be rejected, then calling it a dictature when it happens, and doing it anyway, and there the violence begins. The Amesty report says nothing of this context, I have no idea why (I can guess it probably is because they support the yellow vest movement).