Bahá’u’lláh was born and lived in 19th century Persia until He was exiled to Iraq, Turkey and finally Palestine. Most, though not all of His interactions were with people from a Muslim background. He didn’t have too much to say about Hinduism. Krishna and Buddha were mentioned as manifestations of God, Shiva wasn’t. If Bahá’u’lláh had spent time on India I’m sure He would have said a lot more.Why did your preceptor overlook or forget to mention Him?
He can be forgiven, for even most hindus no longer remember Lord Shiva as a historical person who actually walked the earth thousands of years ago but now see Him only as a god.
The collection of talks 'Namah Shiváya Shantáya' had not yet been written in the days of Bahaullah.
Namah Shivaya Shantaya - Sarkarverse, the wikipedia of all things Prabhat Ranjan Sarkar