Continuity mistake: In the beginning, where it is showing how the Wonka chocolate bars are made, we see trays holding twelve pieces of chocolate. When it shows the trays on the conveyor belt, each tray holds fourteen pieces of chocolate.
Continuity mistake: In the scene when Agustus Gloop gets sucked into the chocolate tube, the inside of the tube is covered in chocolate. But in the far away shot, when you see the tube being retracted, it is perfectly clean inside and out.
Answer: Wonka is simply uncomfortable around people. Gum chewing is simply an annoyance he never had to put up with as a recluse.
JC Fernandez