Having a party is not illegal. And even having an illegally loud party is not a crime unless you refuse to comply when the police come tell you to knock it off.

They wouldn't even have probable cause to search anyone for drugs unless they saw evidence of someone using.

The one person who was arrested only got arrested because they tried to flee and assaulted an officer in the process.

That said, for normal, non-rich people parties, it's common practice for cops to make everybody leave and then wait just outside the neighborhood to bang everyone who drives away on a DUI charge.