Well there is "time and place" in the reasoning behind this. This guy could protest anything at any time of the year on that location except for the 4th of May between 18:00 - 22:00. When there is a none political national Remembrance ceremony on the Dam Square.
Think apart from spending the night in a police cell this guy got no charges pressed.
If I'm only allowed to exercise my rights in times and places approved by the government, they're not worth much, eh? I don't believe any opinions or ideas are so sacred that they cannot be questioned.
Also night in jail without charges pressed doesn't make this better. That basically proves there was no justifiable reason to arrest him, yet he suffered as a result. It's an easy way for authorities to suppress opinions they don't like.
Where do you live? Some states and provinces have buffer zone laws where you cannot protest against abortion providers. People have been fired for saying the wrong things or voting for the wrong candidates. People who live in "free" countries get persecuted for their speech and beliefs all the time. Maybe not by the governments but by the people.
I think you are conflating speech and action. He was not arrested for having that idea, or communicating it.
He was detained for attempting to disrupt a public ceremony.
The right to speech does not come with the right to do it anywhere at anytime.
What makes our countries the envy of the world is that we live in free societies where you cannot be persecuted for your beliefs /s