Going back to the topic, i do believe that the founder of binance could indeed possibly have dumped his coins, but this shouldn't matter much because like any free individual he should be free and allowed to do with his portfolio whatever he wants to. Whats the point of owning something if you can't use it.
The only thing I've seen is a tweet in which the Binance CEO has announced that they are going to move the tokens they own to different addresses, they will not sell them. If anyone has doubts about whether they tell the truth or not, it will be very easy for them to check it on the blockchain.