This holding was possible because California's constitution contains an affirmative right of free speech which has been liberally construed by the Supreme Court of California, while the federal constitution's First Amendment contains only a negative command to Congress to not abridge the freedom of speech.
Because of the Pruneyard case, people who visit shopping centers in California may regularly encounter people seeking money or attention for various causes, including charitable solicitations, qualifying petitions for amendments to the state constitution, voter registration drives, and sometimes a beggar.