The iced mug comes from recommended serving temperature for American Mainstream Light Lagers is 33-40.
Proper Beer Serving Temperatures - American Homebrewers Association
General Serving Temperature Rules:
All beers should be served between 38-55° F.
Lagers are served colder than ales.
Stronger beers are served warmer than weaker beers.
Darker beers are served warmer than lighter beers.
Macro lagers are served as cold as the Rockies.
Serve beers a few degrees colder than the target temperature, to accommodate for warming from the glass and the drinker’s hands.