I guess you really overthink this. You reacted spontaneously and they realized they used the "wrong" language out of habit in this, and then switched to the language you'd understand.

If your Spanish is enough to reply that you didn't understand them you can use it, but as it was a spontaneous reaction please don't overthink.

This being said: If you travel to a foreign country it's the entire opposite! Like if you travel to my place (neither native English nor Spanish) and would use a few basic words or lines, like saying please or thank you in my language, you can be sure I will highly respect this! It doesn't matter if you can speak a lot, or if you pronounce it correctly, but if you try you are above many tourists who automatically expect everyone to speak english.