A link on the front page about a USOTC physiologist helping Willis beat US runners is so overblown. In the actual article it mentions that a physiologist from the USOTC noted a trivial piece of information--that Willis is the only top runner who did not altitude train.
So now Willis will add altitude training. My guess is he would have done it anyway. Also, altitude training is not automatically positive. Lots of people train at altitude and see no improvement. Some people train and see a decline in performance. It takes some trial and error to get it right.
What is Willis trains in NM and then starts to run slower?
Could (and has) happened.