Katy Perry treated her hometown to free booze at a concert this weekend -- but might've spoken too soon ... 'cause much of the crowd went runnin'.
Katy performed Saturday night at the Santa Barbara Bowl for what she dubbed 'Witness: Coming Home' -- a benefit show to help relief efforts for the wildfires and mudslides in the area earlier this year. All ticket sales were donated, including Katy's cut.
End - Performance - Katy - Audience - Drinks
Toward the end of the performance, Katy offered to buy the entire audience "all drinks" on her dime, per eyewitnesses....