Some good info
I am not the expert here, but yes, that is likely “wrong”. As you get closer to Threshold work (SS is the middle area between Threshold & Tempo), you start using more and more carbs/glycogen. These are not on/off switches, but faders of percentages of fat/glycogen use.
The percentage of blending between those energy sources varies from person to person based on their physiology and training history. But as you get into the SS and above work, you are surely using carbs/glycogen at a higher rate than Endurance level work.
Long story short, you need to make sure you are fueled coming into these types of workouts. Doing them fasted (without major food intake just prior) is possible, but relies on the fueling that took place many hours before and any prior workouts.
If you under-fuel after a workout, and take that depleted state into a “hard” workout like SS or above, you will be in for some hurt. But if you properly load the day or night prior, you can do a decent SS workout without “extra” fueling.