You're describing the knee push variation of "Scissor Sweep." It's very common in Brazilian Jiu Jitsu.
There are two main ways to do it from full guard. Both involve getting control of one arm in either double wrist control, or arm drag position. For the sake of this example we'll say you have their right arm.
Method 1: Classic Scissor Sweep
While keeping your arm control, hip off so you're facing the side of the arm you have. You have their right arm, so you're on your left hip. Bring your right knee up to their chest (Z guard position). Drop your left leg to the ground. Three movements happen here at the same time.
- Pull the arm toward you (ideally across the body, but not necessary)
- Kick your left leg in hard, chopping out their leg
- Kick your right leg to the left, moving their upper body over 180 degrees.
You will end up in mount or side control. Worst case is half guard.
Method 2: Knee Push Variation
This is the one you described. While keeping your arm control, hip off so you're facing the side of the arm you have. You have their right arm, so you're on your left hip. Bring your right knee up to their chest (Z guard position). Drop your left leg to the ground and put your foot on their knee. Three movements happen here at the same time.
- Pull the arm toward you (ideally across the body, but not necessary)
- Kick your left foot hard, pushing their knee backward. It will straighten backward causing them to lose balance.
- Kick your right leg to the left, moving their upper body over 180 degrees.
The idea is you switch back and forth between threatening method 1 and 2. They defend method 1, you hit method 2, etc. It's an extremely effective sweep. The main danger you face is someone hopping over your sweeping leg when you drop it to the ground and them taking side control. Be prepared to bring you leg back into your body to recover guard if you fail.
As for the origin, most guard techniques are attributed to Carlos Gracie, as guard was not a common position in Judo until Carlos' adaptation to Brazilian Jiu Jitsu.