In your own words...
"No one knew he was shot, according to Ramos and Compean testimony."
Then...
"Ramos and Compean testified that he disappeared into the brush upon being shot and didn't see him again until someone spotted him on the other side of the Rio Grande, in Mexico. "
Now some may call it it slip of the tongue, others may call it a Freudian Slip of the tongue, I'll let the readers decide.
upon being shot AT.
Don't get your panties all wadded up in a "gotcha" moment.
Shot--shot at. After the fact, knowing he was shot, it is indeed the same moment.