1980 original formula Coke unopened, w/sugar, Physics Mystery! Bonus Pepsi cozy

Description

This can is unopened and mostly full of original sugar-laden (no corn syrup for Passover) Coca-Cola. The Real Thing!
From before the New Coke debacle.
In an odd mystery of physics, the can now weighs 10.5 oz and the sides have pulled in slightly.
How is this possible? If any of the coke could get out, why would it not be replaced with air?
How was a vacuum created in a sealed container?
It has the 1980 LA Olympics logo. Made in New York. One owner; I have had this since before Reagan took office. As a special bonus, I'm including a foam Pepsi two part cozy. It can act as either a drinking cup or as a can holder; when you take the cup liner out, it's the right size to hold a can. It dates to around the mid-80s and thus complements the Coke of Mystery.