I know how busy you'll be but if you could find the time to formally complain I would. People may attend with their children and could you imagine if they heard their parents being told they aren't their real parents (due to sheer ignorance). The damage that could do....
The birth parent is a parent, the adoptive parent is a parent, all REAL parents. Those terms describe only the nature of how they became a real parent and I've never met a person (birth parent or adoptive parent) whose offended by those terms. I do know that I would be offended if I was told I'm not a real parent, because I am one and while I've never asked this question to a birth parent, I'm sure they would be offended if they were described as not a real parent due to no legal rights or time looked after came into it and rightly so, they too are real parents.
Personally, I don't think it's rocket science, people often make mistakes, fair enough, but once you correct the terminiology they then use the correct terminology, not insist onwards with being ignorant to it. However, clearly there are some idiots in the world who need it spelling out and a formal complaint requesting what training will be done to correct the issue and prevent others being treated in a similar manner, may bring cause for a lesson to be undertaken. So sorry you had to experience that 
And combined02 you say..
Moreover, there are some adoptees and "birth" mothers who object very strongly to the term, and so it is unfair to them to push it too much.
Im presuming you mean the term 'birth mother', if so, while I haven't found it to be true myself, in fact with adoptees I've found quite the opposite, if I did find it to be the case I would immediately change my choice of language with that person. But the same respect should be shown to adoptive parents. We don't like the term real parents only being applicable to birth parents as in this case, so it is unfair to push that too much too. I have contact with the birth parents of my children and we both are as respectful to each other with the language we use in our communication because we respect that both of our feelings are equally important.
And I agree it is not really ignorance to use an incorrect term as most people aren't familiar with positive adoptive language so I don't hold it against people when they don't, but it is ignorance to use the incorrect term and continue to use it despite having it explained to you and seeing a person is visibly upset, or maybe that isn't ignorant, just plain dumb. Either way...