I recall seeing this comment as well. Measuring BTC in GWP is an odd concept - maybe I misread - but I take it that means 2 trillion worth of global world product is made in BTC? Or just that BTC price X coins in existence = 2 trillion?
Apparently today we consume 100% of our energy (hah!) for GWP of 78 trillion (nominal) [1]. So 2% for 2 trillion would actually appear to be more efficient. But again, I am not sure if this definition is even real, nor does this math apply.
Maybe this is up there with bitcoin "market cap" or "price to earnings" terminology... :|