Again, this may be a question of politeness. Maybe it was rude, and maybe not. I personally do not think so. I would have thrown down a twenty and not thought a thing of it. But if others have a different take on the etiquette of the situation, I'll accept that.
However, not to beat this to death, the notion that this action on his part was a boundary violation, "unhealthy", and evidence that an entire cohort of people need to be in recovery, is over the top and is exactly the sort of black and white, reactionary thinking that prevents the formation of healthy relationships based on give and take.
I understand that the essence of unhealthy codependency involves over-caring and over-concern about others to the point where we neglect ourselves. But it does not follow that healthy behavior consists of the opposite, where we set up barricades to separate ourselves from others, judge them mercilessly and declare that they are "sick" if they don't meet our expectations perfectly. In my view, when we do this sort of thing we end up in pretty much the same place as we did in our codependency: alone.