According to Axe’s report, he claims that in theory the F-35 should have had the advantage due to the fact that the pilot claimed to have a “clean” configuration for the test, meaning that it had nothing under its wings or weapons bay, while the F-16D had external fuel-drop tanks which would have put it at an aerodynamic disadvantage.
In fact the F-35 pilot had another advantage which was his helmet that was supposed to help the pilot “see through” the plane, thus allowing him to check out angles and corners that the F-16 pilot might not be able to see, but even then it wasn’t enough as the pilot claimed that the helmet was actually too big for him to move his head around the canopy effectively.
This is actually not the first time that the design of the F-16 has come under fire. The co-designer of the F-16, Pierre Sprey, stated in an interview back in 2014 how he felt that the design of the F-35 was a terrible one based on a “dumb idea”.