I do not believe that what they claimed is the real reason. My guess is
that there is something behind it. As an editor, I can read a "confidential
" section to editor only, which is not common in my experience. But I did
have a few cases that reviewers questioned the quality of the work. I need
to draw a conclusion based on that. As a reviewer, I also once questioned a
study and asked more control experiments regarding to the method. The
responses from the authors were the "perfect" answer. It was too good to me
. So I wrote my only time "confidential" section to editor; then we had a
discussion on the phone about it. In that case, we draw a conclusion that
we are not at the position to judge beyond the data provided. However, it
could go the other way if I insisted. The journal that you mentioned is not
the top one. There is no priority issue in my opinion unless you send a
cancer paper to this heart journal.