This is what System76 engineers say. That their motherboards are made by an ODM (Clevo), and Clevo sells similar motherboards to customers other than System76

This is what System76 engineers say. That their motherboards are made by an ODM (Clevo), and Clevo sells similar motherboards to customers other than System76 - but that most other OEMs (other than Apple) have their motherboards made by ODMs, who then go off to sell similar motherboards to other customers. In other words, most OEMs are selling machines built around "repackaged" ODM motherboards, so it is not a trait unique to System76.