I think that there are many elements at play in the novel. I think that there is a narrative story being told from a literary standpoint that integrates aspect of history and philosophy into one forum. The idea of exploring the different cultural valences is one that spans both history and philosophy. The English culture and Indian culture, as both presented in the novel, are ones that have differences in historical and philosophical narratives. To a great extent, Forster attempts to discuss both differences from the cultural standpoints. I am not entirely certain that there is a conscious shift of literary voice or paradigm in the novel to the extent that the statement presumes. I believe that there is a discussion of historical differences and consciousness and a philosophical set of differences and expression of consciousness within the literary story being told.
I am assuming that you are referring to A Passage to India by E. M. Forster? If so, I would have to disagree with this statement. I think this is a multi-layered novel and that history and philosophy are but two of the layers. The historical layer is necessary to the plot and setting. It takes place in India during British colonial rule. The history is an important part of the theme, or the philosophy, because it focuses on the relationship that the British had with their colonies. The historical relationship between these two cultures illustrates the challenges to establishing friendships when the two cultures involved are so very different in terms of language, religion, food, physicality, philosophies.
The novel also has a symbolic level in which history and philosophy go hand in hand. The India of the novel is a country of three religious philosophies: Islam, Christianity, and Hinduism. The Christian Europeans, with a few exceptions, are presented as being very ethnocentric with regard to other religions and in their ignorance, wind up offending Muslims and Hindus. The Muslims in the novel are cultural Muslims and do not really practice Islam (Dr. Aziz) other than on a superficial level. The only true man of faith is the Hindu, Professor Godbole. His Hindu philosophy totally accepts things as they are. Forster seems to suggest that this philosophy is the best approach to life. It also seems to represent the "real" India.
So history and philosophy are both different levels of the themes in this novel, and they work together to illustrate them. You can read about the themes here on enotes (click on the link below and then choose "themes") to expand this theory further if you agree.
Another teacher may give you a different viewpoint and then you can decide what YOU think.