Same difference. If someone has a Windows 10 device and got rid of it, but didn’t purchase a Windows 11 device to replace it, they’re no longer a Windows user. Sure they could have had multiple Windows devices for some reason, but it’s rare for someone to own more computers than they have potential users to operate them (barring things like schools or companies that maintain a fixed pool of devices, although even they try to avoid having significant excess inventory). So yes, fewer Windows devices is to within a certain margin of error fewer Windows users.