I think that you acted quite reasonably until the end, and I see why the other passenger thought you crossed the line.

I know it is easier for some types than others, but when the FA has done everything they can to make things right, and clearly apologetic, at some point you have to accept their apology. If you won't, and berate them about how they should not take garbage without asking, at some point the scale tips the other way and the FA appears to be the victim of a DYKWIA. That is what happened, and something to keep in mind next time.