There's a correction needed here:

Tether had claimed last year that Friedman LLP successfully completed an audit of the company to ensure that Tether has the money to back the USDT tokens the company has issued.

This audit claim has drew a series of criticism with many claiming that no official audit occurred.

The Friedman memo was explicitly not an audit, and Tether did not claim it was an audit when it was released. See their accouncement regarding the memo, which says:

These consulting services do not constitute anaudit [sic] or attestation engagement, which would include a significantly expanded scope of procedures and take substantially more time to complete.

We hope that the community considers the attached memorandum for what it is: a good faith effort on our behalf to provide an interim analysis of our cash position and our issued and outstanding tokens, as part of ongoing efforts to further professionalize the transparency mechanisms of Tether Limited.

That is not to say that Tether have done nothing wrong or suspicious. See this article that I wrote for a bigger picture on the situation.