You can see someone on the left sitting and waiting and someone on the bottom right hiding.
What we don’t know is how long they have been waiting but on the clip you can see the thief’s arm come through hand feel around for something to grab. And WACK just like that the person on the bottom right grabbed his arm and had him trapped.
The second person jumped up to help and not sure what happened next but small vendors work hard enough so when they suffer loss due to theft it really affects their livelihood.