The intention of the revenue to file the tax audit report within prescribed time limit is to enable the AO to complete the assessment of the assessee within prescribed time limit and non compliance of which will lead to penalty u/s. 271B.
Now in your case it seems that there is malafide intention of the assessee to avoid tax liability. In addition to that, the AO can complete the assessment only if complete details in respect of income of the assessee is furnished to him. You can also refer the case of Udupi v. Dr. K. satish Shetty (2010) 188 Taxmann 0032 (KAR) in which the penalty u/s. 271B was deleted as it was established that there is no malafide intention of the assessee. Hence, if one can establish the bonafide belief of the assessee then only there are chances of deletion of penalty.
Further, as per the provisions of sec. 44AB the turnover of various bsinesses carried on by the assessee are required to be clubbed for determining the applicability of this section. Hence, AO is correct.
But wait for others reply one may find exceptional citation.