I think this relates to the amateur vs. professional useage, where it describes someone who does something for money instead of love. It's perfectly understandable for a mother to throw a fit over how messy her kids leave the house or how obnoxious their importunings for input into the menu might be, because she is doing the cooking and cleaning as a labor of love, and has the right to expect some reciprocation. For a maid to get pissy with the guests for similar reasons is uncalled for, because she is getting paid, which is all she has a right to expect, beyond the normal considerations due a stranger one encounters. "Acting professional" imo, connotes doing something to the best of your ability because you are getting paid for it, and doing your best to give honest value in return and demonstrate some pride in what you do. It does not render your occupation or sphere of employment a profession as such, nor you a "professional" even if you do act that way. Using the word professional in the context of "Acting professional" is meant in opposition to like an amateur or dabbler.