"Adam didn't say anything, he's gorgeous and just sat there looking beautiful and smiling. I don't think for one second that he would ever want something like that to happen," the mother said.
"[His minder] just said 'We're in a rush, he's not going to sign those [drumsticks], we've got lots of people'."
The mother said her son, who had been bullied at school, felt picked on by the minder because of his size.
The pair returned to JB Hi-Fi to join the queue to attempt to see Lambert again but the singer had left.
After being contacted by media today, Sony Music contacted the mother and organised for a signed pair of drumsticks to be sent to the youngster.
The boy's mum said Sony was "amazingly apologetic" and explained that Lambert did not want the boy to go without having signed drumsticks.
Sony declined to comment, except to say the matter had been resolved.
Lambert, a runner-up in American Idol's eighth season, has been in New Zealand promoting a new album.