His mother was “distraught” on being told the truth, the court heard.
The boy was referred to the Home Office National Referral Mechanism and it was concluded he had been a “victim of exploitation”.
Siddiqi was spotted by police in Glasgow’s Castlemilk area on 19 September, where he was clutching two phones and seemed “nervous”.
He tried to run off from officers but was caught. One constable was badly hurt during a struggle, suffering shoulder ligament damage.
Police seized almost £3,000 of heroin on him, which had fallen out of his jacket during the tussle with police.
Siddiqi complained that he had also been “exploited”.
A number of offenders have been convicted under the Human Trafficking Act, but this case is thought to be one of the first involving a child being exploited to deal class A drugs for financial gain.
Siddiqi also admitted in court to being concerned in the supply of heroin and cocaine as well as the aggravated assault of the police officer.
A not guilty plea to preying on another teenage boy to sell drugs was accepted by prosecutors.
Callum Hiller, defending, said Siddiqi came from a good background and that others had also been “pressuring” him.
Lord Scott continued his remand in custody as sentencing was deferred for reports.