Again, if you read the article linked by the OP, the bill presented to Milo wasn't for any of the destruction of property, just for the additional police services required to maintain security.
Again, if this were any other major event (say, a sporting event) that needed police, there'd be a bill presented to the event organizers. It doesn't matter that things turned violent at Milo's event - what matters is that Milo's events come with a history of accompanying large-scale protests, thus police were needed. He was billed commensurate with the amount of police that was required.
That's where this matter starts and ends. He held an event knowing that there would need to be a large police presence, and the police billed him for their time. What happened during the event is entirely unimportant.
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Milo wasn't billed by the police for any damages, per the article.