It was a separate data processing engine within Excel developed by another team (SQL server) for the purposes of self service BI (Power Pivot/Query). Most probably, this engine is not used for normal (traditional) calculations.
You mean if you create the pivot table from data in a sheet? It's not needed for that because you'll run out of memory trying to fit any more than about a couple million rows in a sheet first. Meanwhile you can easily load 10s and possibly 100s of millions of rows into Power Query.
