I'm sorry, I do believe it was relevant to your post, as I understood it:
You agreed with the OP. You then gave an example of authors using the 'first in family to go to uni' concept to make their achievement seem more than it is. You take issue with this, as you are aware of some in your circle that had other privileges to smooth their path in life, which you believe negate the fact no one in their family is University educated.
In response, I said that, in general, that phrase was used to refer to people who faced additional barriers (whatever those may be - poverty, lack of parental encouragement, lack of awareness etc), I agreed that not everyone who was first in their family to attend Uni would face barriers and, those that do, won't necessarily face the same barriers. However, these two facts don't change the third fact, that most people who are first in their family to attend University do face hurdles that others do not.
You disagree with what you feel is the misuse/abuse of the term; but the OP just doesn't believe it should be used at all, as she doesn't appear to believe in barriers other than abject poverty/drug addiction. So, whilst I don't see that you do actually agree with the OP, I can understand the distate in what you refer to as the ploy of some people you know.
Off on a tangent, I find your point about privilege in the UK interesting, as there has been a long held expectation in some other countries that a certain social class would go to university. But even where university was neither an expectation nor a possibility (eg. due to cost), a high value on a minimum level of education was held generally throughout society. In 2 countries I'm thinking of specifically, everyone had to be able to read and write before they could attend primary school. Parents unable to prepare their children for school were not viewed in a favourable light and it was anticipated - and highly likely - that these children would suffer in life (unable to get a good job, acquire land or marry; and would probably end up in servitude). I might be making an inaccurate link, but it seems to me that this historical approach and attitude played a large part in the current position of highly educated populations and education systems and results that are envied globally. I do wonder how the UK can create the sort of value in education needed to propel the population forward in the way needed for the country as a whole to succeed.