I thought he said he first thought it was Drew... not that he was convinced. Big difference.
No that's not the how it went. If you read the article, even after Karen told him it wasn't Drew he still thought it was Drew
Actually, I'll quote it for you:
"It was after I spoke with (Mom) that I walked into the kitchen and looked out the window and saw (Holly) and a man dressed in camouflage walking toward the woods," Clint said. "I called Holly's cell phone, and it rang five times and went to voicemail, and I called Drew's phone also, and the same thing happened.
What that assured me was that they were in the same place because neither one of them answered their cell phone"
and then:
"Oh, my God, Clint!" Karen told her son. "That is not Drew! Call 911!"
Karen said she told Clint to get a gun and go after the man. She hung up to call 911 again and reached Decatur County. She still had not told Clint about Drew being on the other side of the county,
and Clint said he still believed the man to be Holly's boyfriend.
and then:
"When I walked out the back door, I saw a small puddle of blood,
and I still wasn't alarmed because who I thought was her boyfriend was dressed in camo," Clint said. "I thought, 'He's killed a turkey up here on this trail behind the house and brought it to the house to show Holly before she goes to school.'"
and then:
"The thing is there was no turkey," Clint said.
"I wondered why they would take the turkey back to the woods unless they were walking back to put the turkey in his truck. I was not worried until the neighbor pulled up and said her son heard screams"
So yeah, I think he was convinced it was Drew until the neighbour pulled up.