I cannot understand why your cabin crew acted in the manner they did, are you sure they realised you were a staff pax?
With only 3 up-grades it is usually possible to find 3 business class meals due to the extra catering loaded to ensure a choice of meal is offered which I presume your airline offers in business class.
Depending on the amount of pax there are usually a few meal refusals too. I have been cabin crew for over 36 years and rarely had to offer economy meals to unexpected extra pax in business, if I did it would have be done with absolute discretion. I certainly would not reveal to a passenger we had staff pax on board (who were entitled to business class) or up-grades for whatever reason.
If you had travelled with me your offer would have been respectfully considered and I would have been grateful that you had made your offer.