What he means is that RSI is a price oscillator, cannot move...

What he means is that RSI is a price oscillator, cannot move past 100 or below 0 in theory from the way the maths is calculated. Anything over the standard 70 is over bought(OB) and under 30 is over sold(OS). Some use 80/20 but price sensitivities is dependent on the parameter with RSI(14) the default from Wilder the inventor of this oscillator.

You have to be a careful using this because oscillators are only useful in a sideway range price action. In a trending price, RSI will almost always signal prolong OB or OS. You can see recently that RSI has been OB ever since price kept rallying. This OB signals a strong trend and does not mean price will start to crash back down to earth. If you observe the 19-22 Sept pullback, RSI followed price down which is usual and then became OB ever since. This is how price moves in a strong rally.

So far today testing the all time high and met profit takers, it is the natural reversal point and I am not saying this is the top. Where it ultimately pullback to is anyone's guess so a shallow pullback before it continues the rally indicate the trend/momentum is VERY bullish. IF it is a deeper pullback then perhaps the optimism is dissipating. Just remember it is the price that influence the indicators and not the other way around.