There might be a pedantic point to be made about ‘upgrades’ requiring more than is required for ‘maintenance’. Maintenance is an obligation anyway so if the old windows were just ordinary windows and the new ones are also ordinary (perhaps only better so far as they need to be to meet current building codes), then that could count as maintenance if replacement was the best way to fix them.
Upgrades could be replacement with double glazed units (say) or just easier to use mechanisms. I would not rock the boat if all or most are happy to have a bit of an upgrade in the course of fixing the windows.
Most likely nothing sinister was meant by the use of the term ‘upgrade’. Most likely it just reflects an expectation that the new windows will be better than the old ones that were in need of repair or replacement.