Japanese curry is not at all related to Thai curry, Thai curry uses fresh herbs and spices and coconut milk instead of dried spices and butter. Japanese curry was likely introduced during the Meiji era by the British who learned about curry in India, as people were interested in exotic foreign food at the time. In the 60's a company started manufacturing concentrated mild curry blocks so people can make curry at home.

OP, can you tell us what region/country you have observed this in? This question seems to be causing some head scratching. Thanks!