No Problem.
Your answer actually provided the reason they might favour the term mute
For others reading this (merely as a matter of clarification)
Nonverbal is usually part of a spectrum of other developmental issues. Non-speaking is merely a colloquialism of nonverbal with the same connotations of being part of other developmental delays.
Apraxia of speech is a very specific diagnosis - so would only be appropriate to use in that specific situation. (much like APD and CAPD are both very specific neurological conditions - APD being more general than CAPD which is even more specific - so all people with CAPD have APD, but only a small percentage of people with APD have CAPD)
Mute is a non-specific statement with no attached "cause". It is "stand alone" in that it very intentionally doesn't imply any other "issues" aside from not producing sounds with the vocal cords. A very good example would be people who have injuries or surgeries which affect their vocal cords, or have a temporary illness etc are considered mute. As are those with non-specific / un-diagnosed neurological or physical conditions - or when there is no clear connection to another condition/Dx.
Hope that helps!