The American citizen released from North Korea: so was he really tortured?

"the doctors appeared to dismiss that theory, saying there was no evidence the young man had botulism. A senior American official said this week that Mr. Warmbier was singled out for particularly brutal beatings while in captivity, but doctors said they saw no evidence of beatings."  I am just trying to understand. So he was subjected to particularly brutal beatings and yet there is no evidence of beatings? Was he beaten with an invisible tool?