Current historians view the 18th Century as part of the modern period (though most of it is the tail end of the early modern period.) So, to the extent that historians in the period of the future under consideration view the early 21st century the way historians now view the 18th, it won't be very hard for them to see it as modern times.
Historians have broader perspective than you give them credit for.
I think historians will be able to figure this one out. Especially when people are aware of it at the time it's happening.