Historian Manu S Pillai says the following in this article

St Thomas himself, it is said, traversed the land, establishing seven churches so that long before Christianity touched even the outskirts of Europe, there were already Christians in India—a little detail that confounded the Portuguese who arrived 1,500 years later and “discovered” brown “natives” wedded already to the word of Christ.

But my American college level history textbook says that the Portuguese set sail to South Asia expecting to meet Christians but discovered "a local form of Hinduism" when they arrived in Kerala. I wish I had the textbook so I could give more details but this all I remember.

Manu S Pillai says in another article that Portuguese were expecting to see an ancient Christian nation in India ruled by a sovereign named Prester John but were disappointed when they instead met a local Hindu King in Calicut.

If (Vasco) da Gama and his men, weighed down by centuries of collective European curiosity and imagination, anticipated the legendary Prester as they stepped on to the shores of Kerala in India, they were somewhat disappointed. For when envoys of the local king arrived, they came bearing summons from Manavikrama, a Hindu Rajah famed across the trading world as the Zamorin of Calicut.

Was my textbook referring to this Hindu king when they said a "local form of Hinduism"? If the Portuguese were expecting to see an ancient Christian nation in India then why were they surprised to discover Indian Christians in Kerala?