That distinction is completely valid, but I think it ultimately misses the point of the “sideloading” discussion.

I think no one would disagree that installing apps on mobile devices via ADB (Android) or Xcode (iOS) is sideloading. But if I toggle the “Allow installing from unknown sources” setting on Android and install APKs through F-droid and other means, is that sideloading? You say no, the Wikipedia article about sideloading says yes. That also circumvents security features of the OS to install software. The difference comes down to whether or not a mobile OS provides an easily accessible setting for developer tools that facilitates the installation of software from other sources to the point where it becomes possible to automate it in a store-like fashion. It’s not a hard distinction and more like a continuum of how many hoops a user has to jump through to install and maintain software from other sources.

I think it’s useful to think of the “sideloading” discussion mainly from this user-oriented perspective. The technical distinction of needing versus not needing a separate device is technically valid, but it misses the point IMO.