Why do you change the actual interpretation of what was said there?
Selfish mining attacks start to become significantly probable when a node or a group of nodes control at least 28% of the network's computational power
It's not that an attacks requires only 28% it is is just that at that number it stops having so many zeros after the dot that it becomes a possibility.
Again missing from this is that while you could theoretically in secret mine temporary a longer chain with each new block your chain would need to have your chances go down proportionally to the hashrate you hold. That's why the 6 blocks confirmation! (Which most don't care anymore at all)
And how is attack going to unfold, you're going to deposit and withdraw to Binance every hour while hoping in the same hour you're going to finally manage to get the attack ready? And you're going to do this every hour for 20 weeks till you finally get it?
Ghash doublespending happened on unconfirmed transactions.