I've frequently been told that I must be Irish, or that there must be Irish in my ancestry, because of my singing and songwriting.   I take these comments as huge compliments. Most bizarrely, having had the conversation to explain that there is in fact no trace of Irish in my family tree, I was told that in that case "in a past life you must have been Irish".
Probably a fair cop, guv ....
But Dick, the only reasonable response to your experience is to assume she just hadn't met many English people and still fewer who were in any way performers of music. It happens!

Anne