mppt vs pwm

We've been thru that with the fake mppt controller that pulses in bulk to make one believe the input voltage is higher since off is 21v and on is Vbatt, the ave is higher than Vbatt. I see in/out the same till Vabs then my meter goes nuts on the input occasionally reading 21v then back to 14.8 then 21 then ... as the duty cycle is less than 100%

https://www.youtube.com/watch?v=la-gvy0DfJs about 6:30