I remember seeing these bikes (or ones just like them) on the track. Look closely at the front brakes. The calipers were attached to carriers that pivoted near the wheel axle. Behind the calipers there were struts that went up and attached to the bottom triple clamp.
When the rider grabbed the front brake lever, the caliper carrier was forced upwards by the rotor rotation. This would in turn push upwards on the triple clamp and keep the fork from diving.
Primitive but effective anti-dive.