Lewd act in a private booth? I don’t get it!

I just don’t understand stories like this one:

Nick Stahl Arrested at Porn Shop for Alleged Lewd Act

So, this guy, who also happens to be an actor of some repute, goes into a porn and sex shop and gets busted for touching himself in a private booth. 
Why? 
This sort of situation has happened numerous times over the years, and has ruined careers and lives. I still don’t get what is at all criminal in this situation. He was in a booth, I presume with a door. He was watching some porn and getting off. In a little box of a room. Noone in there with him. Again, I presume, no windows. 
So why is this an issue? 
Why can’t someone go and have a release away from the public, away from home, away from everyone and everything? 
What are those little boxes for if not to jerk off in? Oh, right, it is to preview the films you might be interested in purchasing. Right. That’s it. 
Ridiculous. 
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