If an employee already has an EPF account from previous employment, does this mean the old employer maintains the account?

The an EPF is never held by an employer. It is always held by the government (provident fund department) who manages that fund. An employer only facilitates contributions to the EPF on behalf of the employee and the employer itself. Furthermore, once an employee resigns from an organization, the employer will note the employee's exit from the organization on the provident fund portal.