I don't think its the reason for depeg. Binance is not directly linked to tusd (like it was to BUSD), from what I know all they did, that might point at potential partnership is fee reduction while trading on BTC/TUSD and TUSD staking in lauchpools. But it seems to me more like a desperate attempt to move the volume from USDT to avoid a situation where the entire market (and thus binance's business) depended on 1 stablecoin rather than proof that they are connected
And as for trying to keep BNB above $200, binance is burning $600M in BNB every quarter, which is 7% per year. And its only a 20% of their profits which they claim are mostly in BNB. Binance officially gave up the rigid 20% it guaranteed during ICO, but when I talked to a binance employee from the Polish telegram, he said it was due to the legal problems that such a fixed target caused, and 20% is the value they try to stick to. So from pure profit they can buy all existing BNB @200$ in 3 years so I don't see a reason why should they protect 200$. its not a highly indebted company that needs additional financing by issuing new shares at the best price. Its not a shilled shitcoin like luna that will collapse if price drops.
Also there is no increased volatility on BNB today. it's pretty much flat for last 2 weeks.