“Concern” in this context is an Improper Noun of sorts https://news.ycombinator.com/item?id=32673100 It’s academic speak for ‘I believe this may be incorrect’, and it’s very common to use this word in reviews. The reason “concern” is used over “incorrect” is partly to avoid a direct accusation, which can and sometimes does turn out very bad for the accuser. Note that it was not Semenza who wrote about the “concern”. In addition this word can help establish lack of culpability by the journal and/or publisher after the fact.