I read the original comment and (before scrolling down) was tempted to chime in that 'in this context, shrinkage means "theft"' before realizing the discussion had already been had.

I could very easily see someone as having read that as physically shrinking in size, perhaps due to compression by repeated handling, as would happen in a store, or heat or other uhhh... harsh environmental factors commonly found in retail establishments. (Sorry, I couldn't think of a second good excuse)