A few corrections...
3. In reference to beef, if you are talking about Wilson, the beef was tested.
The USADA did not say anything about testing the beef. They said they "relied on reports from...experts on zeranol in the food supply..."
Here's the full paragraph on the grounds for their decision from their press release. The only lab work mentioned is Wilson's drug test, which showed a very low concentration of zeranol in her blood:
During its investigation into the circumstances that led to the positive test, USADA gathered evidence from Wilson, which included reviewing her dietary habits and food purchase receipts. USADA also took into consideration laboratory reports demonstrating low parts per billion concentrations of the prohibited substance in her urine, as well as the fact that she tested negative one week prior. USADA further relied on reports from multiple independent experts on zeranol in the food supply and environment, including the use of zeranol as a legal growth promotant in beef cattle in the U.S. Based on the totality of the evidence, USADA concluded it was highly unlikely that the presence of zeranol in Wilson’s sample resulted from a source other than zeranol contaminated meat.