If he was not a member of EPF before he joined your establishment, it should be presumed that when he joined his previous establishment, his salary (PF qualifying salary) was more than Rs 15,000. As such, he was not entitled to be part of the Pension Scheme. However, that company did not declare him as an excluded employee but covered him under EPF and contributed the entire 12 percent of the employer's contribution to his PF along with his contribution without bifurcating it (employer's contribution of 12%) as 8.33% to the Pension fund and the remaining 3.67% to PF.
Now he has joined your establishment and declared (in Form 11) that he was a member of PF in his last establishment and provided the UAN. Based on this, you can also follow the same practice and contribute the entire 12 percent, being the employer's contribution, to his PF instead of splitting it between the Pension fund and Provident Fund at the respective rates.