I think the point is that they actually surveyed them every two years, so they weren't asking them to look back on their lives, they actually had that information while they were experiencing it.
There may be other biases and errors, but I don't think your argument is valid given the method.
They started surveying them when they were at Harvard from what I understand. That is still quite a bit removed from their childhoods. In any case the point about correlation != causation stands. The information is interesting, but I find that too often with these studies a correlation is taken. A conclusion is then made on the basis of the correlation, and then the conclusion is stated as fact. Anecdotal evidence follows and that's the end of it. The thing that irritates me the most is that it's just taken as truth and rarely if ever do people investigate further. I'd just love to have a discussion about the data and the possible implications and other explanations for the same data with judgement left up to the reader.
I think you'll always get that in the pop psych pieces; they'll always always try to reach some eye-catching conclusion title to pull people in. I haven't read the original paper, but I highly doubt they made a case for causation unless the statistics backed it up; and if the stats did back it up, then the science does in fact say causation and not just correlation. It would be interesting to check.
There may be other biases and errors, but I don't think your argument is valid given the method.