this seems a rather dangerous and naive optimization to me

The optimization is a red herring; it's not changing the result in any way. If the left operand of the && operator is true in boolean context, then it returns the value of its right operand, whatever that may be. Expecting it to return the left operand is wrong. (What you really were expecting is a different parse, based on different operator precedence. (See my other post downthread.))