There's a number of issues here.  One is that when a political leader -- that is, someone with the demonstrated power of a large following -- expresses what ought to be done, it is not at all absurd to believe that a group acting under that leader's name has the ability to at least make a good attempt to bring it about, for better or for worse.  

But there is another issue here with Aristide as as a political leader which calls into question his credentials to represent anything like the "Aristidism" invoked by the author. There are just too many leftist Haitians -- people at known hangouts for the world's progressive diasporas, such as New York's New School for Social Research, that actively opposed Aristide and did more to bring about his overthrow in 2004 than the US did by not intervening on his behalf. It could be, as you seem to suggest, that there are progressive ideals which go beyond the person himself. But it could just as easily be true that those ideals were fictions of political propaganda in the first place, given the poor outcomes when Aristide was given a chance.  

Remember, not intervening on behalf of someone is not the same kind of imperialism as intervening directly to remove someone.  The former requires that the subject fail on his own first, and Aristide's projects appear to have failed largely on their own merits before any blame can be leveled at the US for not intervening a second time to keep him in power.