In Infernal Affairs 1, how did Andy Lau send a message to Ceng Zhiwei that there was a mole? The cell phones of a large group of people around him all show "there is a mole"

Hong Kong police special channel, and Andy Lau back and forth to exchange that channel. Tony Leung Chiu Wai used the Morse code of his finger to tell Huang Qiusheng the new password, while Andy Lau was undercover. Seeing that Ceng Zhiwei was about to expose all the areas he had locked up with his notebook, he sent a mole to terminate the transaction. So someone in that area will receive the message, but have you noticed that Andy Lau pulled the card out of the computer soon after sending it? He actually used his own.