Remarkable you write this, Kaki-san. In Calcutta, when we were children, in several of our celebrations, we used to eat as part of the celebratory lunch or dinner, this pink coloured ginger pickle ("gari" I understand in Japanese). This would be served in only specific households, who were traditional merchants, many of them sea-faring. Their maritime history would go back centuries, and it is believed that such merchants would take their merchandise from Bengal to all over South East Asia and beyond. In Bengal, such merchants were referred to as "Benes".
When this happened, we did not have Japanese restaurants in India (Calcutta where I grew up).
Many years later, when I first tried Sushi in Narita airport, I was surprised to see the exact same ginger pickle we used to have in our celebratory lunches in India, and I wondered how did they come about? Possibly, our sea merchants learned them in Japan and took them to India, or possible that they took their tradition to Japan. Who knows?
Even otherwise, pickles are a huge part of Indian food as well. Indian food, as you may know, have several different regional variations, so much so, that speaking of a "monolith" Indian food does not make sense. The traditional Bengali food, for instance, is very similar to the food you will eat all over South East Asia. Bengal, in this culinary sense, is almost the Western most end of South East Asia. But all over India, from Bihar to Punjab, from North of India to the tips of India in the South adjacent to the Indian Ocean, we eat pickles in various forms and of different types: these could be green mango pickles (favourite in Bengal and parts of South India), vegetable and fish pickles, and so on. These are eaten with meals for the same reason you cite in your article.
The contribution of Buddhism is completely understandable here, as in Buddhism, frugal, responsible meal is widely practiced. Buddhist "Bhikkhus" or mendicants were also dependent on the alms as food given to them. There too, the frugality of the meal and the simplicity mattered, and pickles were perfect accompaniment of such a meal.