I feel a little bad, but I laughed out loud at this.

A lot of Americans are simply not exposed to other languages and haven’t really conceptualized them properly. In their minds, there are two modes of speech — “language” aka English, and “foreign”.

(Another more charitable if more unlikely explanation is that she is a polyglot and she is code-switching. I speak several languages, and fairly frequently a word from a wrong language just pops out.)