Not quite. There's a check in map to see whether the input is a TEMP or not and if so, it is re-used for the output. The list assignment operator also notices that the input is stealable and steals the scalars away to be the kept-for-real copies in @sorted_data. So one copy is made.

I'd have written this one as a GRT or tye's fast, flexible, stable sort, though instead.