Here's a teardown of a recent BYD rear drive unit, performed by Paul Turnbull -- lead engineer at Munro and Associates. https://www.youtube.com/watch?v=4LfDuyqmsts

In very broad strokes: It's just a BLDC motor, some driver components for those spinny-bits, plus some water cooling passages and gears. A surprising number of these parts are identified as having been provided by Borg Warner.

That's nothing like what you describe at all.