Professionalism is a bit more than the improper use of a word or too (or is it two, or to?)
Well, yes, we should all be able to forgive the occasional slip, as we would the occasional slightly bounced landing. But,
When the language we have inherited is eroded by chronic carelessness, that deserves comment. We demonstrate "professionalism" by always working to be better - in everything.
If I observe a person being careless in one thing, I will assume they are equally careless in everything.
So, if I were to observe a flying instructor who does not care to use their language with care while teaching, I'm going to assume that they also do not fly airplanes with care, and why would I want to study with them if I have a choice of a more "professional" one? Yes, I will, in part, judge the quality of a pilot's care in flying by the care with which they speak.
Working life, is to a large extent a continuing job interview, so you may as well conduct yourself as if it is, and present your best image....