Sat Bachan means 'The True Word'. The author, Mirza Ghulam Ahmad Qadiani, tries to upset two of the major Indian religions -- Hinduism and Sikhism -- at the same time. By using the words of Pandit Saraswati about Guru Nanak out of context, he launches an attack on Sikhism by using the words of the Hindu pandit. The author shared his hometown of Qadian with the Sikh community and did not want to upset them too much.
The author's central thesis is to present unfounded research based on an apocryphal relic, the Chola (cloak) of Guru Bawa Nanak, which is presumably kept by the Bedi Sikh family in Dera Baba Nanak in District Gurdaspur, India. The Chola is covered by Quranic verses. Sikh adherents do not consider this cloak to be part of their religion, but merely a gift from the Muslim ruler of Baghdad who finally had offspring due to the prayers of Guru Nanak Sahib.
Needless to say, the book was never translated into Punjabi or English as it was countered immediately by a treatise on the subject by Sikh scholars, Chola Sahib by Seva Singh (18MB PDF) who concludes:
Mirzai friends, if you desire debates then become researchers and then learn how to use your intellect. Otherwise, there is no benefit of such pointless utterings except widespread ridicule. (page 16)
... the Mirzai Party has been shut up [on this issue] forever. (back title, review by Master Autam Singh, B.A., Khalsa College, Amritsar)
Quite aptly, Mirza and his followers have been silent on this research ever since.
In addition to several apocryphal references about Sikhism, the author also includes English quotations from The Dictionary of Islam by Reverend Hughe that merely show the influence of Islam on Guru Nanak's teachings.