For example: I own a multiroom speaker setup not made by Amazon that is Alexa-enabled, all speakers could run Alexa if I had set them up for it (which I won't, ever), and they're very likely counted on this metric. I can remember a multitude of other speakers and devices with an Alexa-enabled badge on their packaging that aren't made by Amazon.
It'd be good to have hardware figures for sales of Amazon's own devices.