When Famous first came to the pet shop, it was told that Old Time Tea was a good fighter, but hadn't got the chance to witness it firsthand. After seeing how Old Time Tea was rushing, it thought it'd have the chance to see it today.
Famous knew Old Time Tea was skilled enough to beat the leader of the gang as well as the other two brothers. But, on second thought, Old Time Tea wasn't elfin yet, it was just a Dragon Li that happened to know Kung Fu.
Famous didn't know the whole story.
Foshan was a place famous for its military art. It didn't matter if they were children or senior citizens, all kinds of people knew something about Kung Fu. Plenty of Kung Fu masters were hiding in the crowds, so even though they were robbers, they had learned Kung Fu professionally. They probably saw competitions all the time so that they could steal the skills. Plus, they were all strong men with knives, they weren't like the seven Rainbow Fighters who broke into the pet shop.