Doubling up is a risky strategy, but it can yield large returns (investopedia.com).
Double Up is both a term for a risky but potentially powerful investment/gambling strategy on the stock market or in the casino, and it is, of course, the term for what you get during happy hour in a bar. In this piece the term is meant to cover a similar range: From the drunken and sloppy but deeply felt sing-along to the more musical "power of unison" and the potentially rewarding effect of opening up something familiar for reinterpretation and re-experience by distorting or emphasizing its different elements or by presenting it in a new context.
The form is simply two halves exploring two types of linearity with the same material: The linearity of a trivial narrative and the linearity of the inherent musical qualities in the very same sounding snapshots.