Walcott's 20-yard cracker was his first England goal since his hat-trick against Croatia in 2008.
He told The Sun: "I think I surprised myself. During the warm-up I put three goals in the top corner past Jack Butland and he wasn't too happy about it.
"I thought it took a deflection which is why my celebration was little bit odd. But I've seen it again and it didn't.
"I didn't know I had that sort of Ronaldo dip in me so I should try it more often.
"I scored at a crucial moment in the game because they'd just scored. I think that shocked them and, from then on, we showed what class we've got.
"It was a tough game and I think we were a bit unlucky to be 2-1 down. But it shows the character we've got. It's not just about the 11 that start if we are going to go far in this competition.
"The boss has already said that. You have to be ready to come off the bench and play the part. So I'm very happy."