Answer to Question 1
To keep the temperature from escalating too high, which may result in scorching or formation of undesirable lumps.
Answer to Question 2
Coagulation of protein and presence of cocoa butter in the homemade beverage contributed to the thickening; Coagulation of the protein contributed to thickening of the commercial beverage.
Answer to Question 3
Presence of cocoa butter in the chocolate and absence of cocoa butter in cocoa.