I was sincere, because as you point out, the phrasing is not actually ambiguous here. There is only one way to interpret this that is coherent and sensible. The usual % shenanigans weren't even on the table for me.

Not that I'd have ever seen "reduced by 0.5x" or any other value below 1x, probably for this very reason. What I do see is "reduced to 0.5x", in which case you're supposed to swap the division for multiplication.

Percentages on the other hand are a whole another can of worms, even if these forms are principally interchangeable, and I find them a lot more confusing a lot more often.

Not that this would explain the whole mean/geomean thing.