The incentives at work here are that if a CEO of a public company makes false statements of this kind goes to jail.
This is like the CEO of the bank that held Bernie Madoff's money going on record before Madoff's fall saying he holds Bernie's money and it's all there.
If Tether is unbacked Howard Lutnick is going to jail, so it is irrational to believe Tether is unbacked at this point.