He said: "Villa fans were brilliant to me. That bizarre goal put me on the scene - we needed the results ourselves and it was a tense derby, 1-1 at the time when I found myself up in the box.
"The ball was up in the air and just out of instinct, I volleyed it. I thought if I waited for it to come down it would be cleared, and if I jumped to head it I wouldn't get enough power to trouble the keeper.
"It was amazing when it hit the net. I'll never forget that feeling - it wasn't the winner, but it was the turning point, and in front of the Holte End. You couldn't write a better script if you tried.
"It went crazy. As I ran to the fans everyone jumped on my back and I ended up in the crowd. So I thought, 'well, I'm in there now, enjoy it'. I'll take a yellow card for a goal like that."
Cahill, one of Bolton's three former Villa players with Gavin McCann and Jlloyd Samuel, had been at Villa since he was 13.
He said: "It was hard to leave, but I needed to establish myself in a team."