I don't think the other poster was objecting to the excitement about this being a potentially important discovery, or criticizing the research or the researcher

I don't think the other poster was objecting to the excitement about this being a potentially important discovery, or criticizing the research or the researchers. They are objecting to the way the linked article presents it, specifically its claim that "Courchesne and Muotri have established that brain overgrowth begins in the womb." As readers of this article we can fill in the blanks and imagine that there might be a well-understood and well-founded way to extrapolate observations of these BCO samples to fetal brain development, but we can equally well imagine that this extrapolation might be tricky or unreliable. So as lay readers we're left to guess which mistake the author made: did they overstate the conclusion based on a bad assumption, or, after already explaining so much about the research and connecting so many dots for the reader, did they forget to explain why we can confidently draw conclusions about real fetal brains from these in vitro models? Obviously the second is more forgivable, but it's annoying either way.