So, I have a friend, Joe Bob, who makes a bundle of money in the stock market. He sells his small Brooklyn apartment, and buys a mansion up the Hudson river, with an extensive "park" around it, of the sort where scattered large trees are set in acres of lawn.
How might I explain this? Well, one thing I might say is, "This has been a goal of Joe Bob for a long time: he always wanted a mansion with some grounds like that, and now that he has the money, he values achieving that goal more than anything else he might do with the cash."
That is a fine explanation. But here is another explanation: people's appreciation of such settings comes from the fact that our ancestors lived on the savannah for many, many, many generations. Therefore, it is in our genes to like such scenes: they make us feel at home.
And here is yet another explanation: European nobility possessed just such manner houses in just such natural settings for hundreds and hundreds of years. Therefore, we are socially conditioned to want to acquire such property as a sign of our prestige and status.
The first explanation is an individualistic one. The other two are not. But all three are, I think, fine social explanations, and any one of the three might be superior, depending upon the context in which one is doing the explaining.
Now, does your version of methodological individualism insist that only explanation one is valid? Then it is false.
Or do you claim, "No, methodological individualism, as I use the term, can encompass all three explanations"? Well, then it is empty: if it doesn't proscribe some sorts of explanations of social phenomena, then it is silly to call it "methodological individualism."