Greatnan, I cannot comment on your experience, I wasn't there but setting your experience aside, I have heard the same so many times from people who move/visit Wales . What does puzzle me is these complaints have always been made against the Welsh in North and West Wales, as Welsh is the first language for many in the north, why would they converse in English then switch to Welsh , in my experience two people who speak Welsh converse with each other in Welsh not in English.
Is is not similar to saying I was in France and two French people were holding a conversation in English but when I approached them they started to speak in French, makes no sense sorry