Even if Windows did contact the Microsoft activation server, as long as it is on the same computer the Installation ID will match what is stored at Microsoft and the activation code will be returned. The Windows 7 activation information does not get changed in any way when the upgrade to Windows 10 is done. The Windows 10 activation is also stored at Microsoft when the upgrade is done. So, if the same Windows 7 on the same computer does contact Microsoft, it retrieves the Windows 7 activation code. If the same Windows 10 on the same computer does contact Microsoft, it retrieves the Windows 10 activation code. It does not matter how many times or how often this occurs so long as it is the same computer.
Move the hard drive to a different computer - the Hardware ID changes, therefore the Installation ID changes, Windows revokes it's local activation and contacts Microsoft. Depending on the type of product key (retail vs. OEM) and the number of times new activation has been requested, either a new activation code will be issued for the new computer - or a refusal code will be returned and the user will be prompted to call Microsoft for activation.