I think it would come down to tire size, if there to narrow to safely handle some off roding, I would not call it a Hybrid !
If there to big, I would call it a comfort cruiser, I Think they are supposed to be a cross between a Mountain Bike and
a Road Bike, so they need to be able to both, just will not be the best at either but are great for people like me that,
might go for a 10 mile road ride, then 5 miles down a gravel road. (AND YES) a beach cruiser could do that, but not
like something with 21 or more gears, smaller tires, and possibly suspension, Hybrids should preferably have the lock out type
for when they are own the road......Richard