Castroneves was acquitted Friday of the tax evasion charges, along with his sister, Katiucia Castroneves, and his attorney, Alan Miller.
Miller also is Johnson's attorney, so Johnson had a sense of relief when his longtime adviser was cleared.
When Johnson heard the news, he called and left Miller a congratulatory voice mail. But he also left a two-word text: "Hell Yes!"
"Alan has taken care of me for a long, long time [13 years], and he's done an amazing job," Johnson said. "I'm glad the judicial system was able to work itself out and they were able to prove their case.
"I'm just happy for everybody involved. I know it's been extremely tough on all of them. I can only imagine what was going on in all of their minds with potential jail time and what that would mean for careers and lives."
Johnson testified as a character witness for Miller during the trial in Miami.
"The first four or five years with him he never even sent me a bill," Johnson said. "Alan has been someone I could go to for advice of so many things, like buying a home or getting insurance.
"But in general, he's a big part of my team. He's always shown the utmost respect and integrity. I'm happy the jury was able to see that as well."
Miller, 71, is a former professional football player who has practiced law for 44 years. He represents other racers, including Clint Bowyer, Casey Mears and Danica Patrick. But no one has been with him longer than Johnson.
"I know what Alan and his family have been experiencing," Johnson said. "Hopefully he will take a long vacation and let that stress find a way out of his body. It's been very difficult. For a man of his status at his age to experience something like this so late in his career has been very tough on him."