They laughed. Apparently picking up Spanish from your Spaniard friend has some downsides.
As in South American backpackers find it funny/amusing this drunk Chinese guy in an Australian pub used the Castellano equivalent of "y'all" in a sentence.
They were ultimately nice about it, much better than the time my (English speaking) Canadian coworker tried to speak to some Parisians in school level Québécois and they scoffed and continued in English.
It would be more like if most British people still use thou and insist Americans, Canadians, Australians, etc are wrong for not using thou.