You're confusing RNG manipulation (really clearly bad, basically cheating by removing the randomness from the game) from RNG prediction (less bad but still unfun, being able to predict future random states).

You can be safe from RNG manipulation while still suffering from RNG prediction. Players can't modify the events that are going to happen, but if they can predict them, it's still a problem.

The situation is like there's a bug in the blackjack table where, instead of shuffling the whole shoe together, each deck in it was shuffled on its own in the same way and then the identical decks are stacked together. Once you've seen 52 cards, you know the repeating pattern and can play with perfect or near-perfect knowledge of what's about to be dealt.