Wow - that must have been quite something, to see the app change like that. Do you have an Indian mobile number registered to your Google account by any chance? I don't see how it could switch to the Indian version since the Indian version is so closely tied to having an Indian mobile number.

FWIW, I did not notice any changes to my Google Pay app (US-based). The interface looked exactly as it always does and it behaved as expected with my US-based credit cards. One caveat - my app just recently (in the last couple of weeks) switched to the new interface that combines the old Google Pay and Google Wallet apps in a new presentation - Google has been rolling this out to everyone recently. It's possible also that your Google Pay app behaved differently if it hasn't yet been "upgraded" in this way?