One other thought comes to mind--the submission pattern of different subfields of science vary tremendously. There are also questions of expediency--for examp

One other thought comes to mind--the submission pattern of different subfields of science vary tremendously. There are also questions of expediency--for example, perhaps a student was graduating and they decided that the work would be published quickly in scientific reports, or perhaps another group was rumored to be publishing soon. It's impossible to say. If it were my field, I would just read the paper myself to see if it were technically sound instead of stressing too much about the fact that it's a scientific report. If it wasn't my field, I would check to see how cited it was in the future...