There is no evidence that Squanto became a Christian when he lived with the English monks in Spain. He did learn to speak english and he was taught the gospel story by the monks.
Also, he alone didn’t help the Pilgrims to survive, they were already catching fish, lobsters and doing some hunting of the local game animals by the time Squanto showed up. Squanto’s importance was that he was able to speak English and help bridge the friendly relationship the Pilgrims had with the natives, especially the head sachem, Massasoit, who’s Wampanoag Tribe were the main source of helping the Pilgrims to survive. Also, the Pilgrims survival when they first arrived, which was out in what is now Provincetown on Cape Cod, was by steeling the corn that a native had stored for his family in an underground bunker. They later compensated the man with modern goods of the time, i.e. pots, pans and steel knife.
Squanto also tried to use his knowledge of English in order to become the head sachem and used deceit to try and accomplish this, He plan was discovered by both the Pilgrims and Massasoit and the latter wanted his head. The Pilgrims actually saved Squanto from the death sentence.
Also the OP article is wrong in that the Pilgrims, were not Calvinists, but Religious Separatists with a belief system of their own. Of the 102 who arrived on the Mayflower, only half were Separatists, the other half, were merchant adventurers who belonged to the Church of England back in their homeland.
It was because of the differences in religious beliefs that both the Separatists and Merchant Adventurers, after arguing about what laws would be followed once they got off the Mayflower, ended up creating a compromise known as the Mayflower Compact. This meant that William Bradford head of the Separatist, would enforce laws according to the Separatists beliefs, once they landed, and only within their own settlement. This meant that the Merchant Adventurers would quickly seek to set up their own settlement further north, near what is now Boston,
As a result of the Separatists beliefs, Christmas on December 25th in 1620, was celebrated by the Merchant Adventurers, not the Separatists who did not celebrate the holiday, because it wasn’t in the Bible to do so.
Anyway, read the book, “Mayflower,” by Nathaniel Philbrick for a accurate history of the Pilgrims arrival and through the Indian Wars.
Jim