In general, a seconded worker is one who is assigned from a foreign company to work for the local (UK) company for a limited period of time for a variety of reasons.
As far as the auto-enrolment [AE] regulation is concerned, we just need to confirm that the seconded worker's contract of employment is with the Indian company and that they will be going back to India after the work period (secondment period) has been completed.
If this is confirmed, then the UK company does not need to assess the seconded worker and auto-enrol him/her into the UK company's pension scheme.