We tend to think of things as discrete entities with clean demarcation between individual elements a bit like the sharp steps in effort on the Ramp Test but as @SeanHurley pointed out workouts are really on a continuum. Also our bodies don’t see step changes in how they respond to the stimulii in the workouts, even an endurance workout down at 70% FTP has some VO2max component for example, it will be very small but it will be there.
So rather than think of each zone being distinct think of them as a series of overlapping bell curves and somewhere around 105-106% the proportion of threshold to VO2max tips in favour of the latter and so that’s how it gets classified.