The update channel doesn't affect your licensing status. It only determines the level of testing that patches must receive before the updates will be available. Your perpetually licensed Office software will only receive security updates and bug fixes, no new functionality will be made available. The Office 365 products will receive security updates, bug fixes and feature updates. Your update channels must match because Office 2019 uses the Click-to-Run installer and has shared libraries with the rest of your Office 365 suite. If they weren't on the same schedule, your products would give conflicting information about which updates should be installed. More information is available in the Microsoft document you linked in your question: -us/deployoffice/office2019/update