(CNN) -- An "America's Got Talent" contestant's emotional story of getting hit by a grenade in Afghanistan is not backed up by military records. And now, questions surround whether he embellished his heroic tale. 

Timothy Poe wowed the three judges on the NBC program Monday night after stuttering when he spoke, but singing "If Tomorrow Never Comes" without a hitch. 

He said that the stutter was caused by the grenade attack and that he didn't really know he could sing until his speech pathologist told him to try singing in the shower. 

After receiving an emphatic "yes" from each judge, advancing him to the contest's next round, Poe walked offstage and told host Nick Cannon, "Oh my God, it's amazing. I was so scared up there I c-couldn't remember where to put my fingers. I was like, oh I didn't know." 

"I don't know if you just noticed," Cannon responded, congratulating him, "but this whole sentence that you just said you didn't stutter one bit." 

In an interview Tuesday with the "You Served" podcast, Poe said he does not stutter always, "just when I get stressed or nervous or something big happens." 

On the NBC show, Poe said he served in the military for 14 years. In 2009 in Afghanistan, he said, he was struck by rocket-propelled grenade. "By the time I turned and went to jump on top of my guys, I yelled 'grenade' and the blast had hit me," he said. 

The attack "broke my back and gave me a brain injury, so that's the reason why I stutter a little bit," he said. 
How many, then?
Timothy Poe wowed the three judges