I wouldn't argue that the purchase of the car was a good financial decision. As a side note, I don't think buying a C-class Mercedes is EVER a good financial decision. The reactions to this article (or that OP experienced in the narrative) are a testament to the success of Mercedes establishing themselves as a luxury brand even though they sell econo-box line vehicles (top post right now puts this pretty well; this is a symbol of wealth, not actually much of an asset).
I think the house was a worse decision, as it implies a longer confidence in earning potential; the car could have been paid off much more quickly, and we don't really know their earning power at the time of purchase (though I doubt it'd help the point of them being fiscally responsible).
I think a big part of this article is trying to cast an empathetic light on people that end up in tough financial situations BECAUSE of bad financial decision, despite having come from opportunity. When considered clearly, even those impoverished that did not come from opportunity could be saddled with the blame of 'bad financial decisions', but just have many more justifications (that are more easily empathized with) for making the decisions they did.
At some point or another, though, you are following the same mindset of the 'root beer police' in the line at the store, written about in the article. You are drawing a line saying 'you purchasing THAT is not responsible', and you feel justified in doing so because they are using public help.
That's sort of the debate at hand here. Is the use of public funds an invitation, or justification, for judgement from others on your consumption? I believe that it is; if you are going to take money from the government, one cost you suffer will be unyielding judgement from others on what you do or do not buy.
My point: not selling my old(er) Mercedes in lieu of taking food-stamps while I find another job might ACTUALLY be the best financial decision I can make, for a number of reasons. Whether or not I feel morally reprehensible about this is my own business, really; the assistance programs have their own requirements for eligibility and if I meet them, I meet them. Despite this, it is an invitation for judgement in the cultural climate in which we live, and that's just how that is.