I don't think there's a particular relationship between USDT anew bitcoin.
The amount of USDT in circulation appears to have an effect on price of cryptocurrencies, it's not a steady pattern, but the higher amount of USDT created rises the price
It is normal for some to always look for a reason why the market is down but in the real case of things, market is down because traders and people are selling more than buying, and I do not think we should be looking for more explanations than that. USDT is a centralized currency that is backed by fiat of USD equivalence. Printing more out is just a way to compensate the demand and since according to the team, it is backed by real funds, then I see no reason why that would be an issue for any market.
I think in Tether people are just looking to find reasoning and causation which is not there. People like to look for a scapegoat and a lot of times they fall on Tether.
Yeah, that is the problem here. Market goes down and people are wondering why the market is going down and even if they end up finding irrelevant things which could have been a coincidence but in reality, cannot affect the market, then, they just say it anyway. I see nothing here that depicts what the OP is saying to be right. The market just wants to go down, so deal with it and focus on the things that matters.