[propbeanie]

That looks to be an old report, either via radio (most likely) or via radar, of a large group, whether merchants or warship. If you click on it, it might tell you "Large group, heading SSW, Medium speed" or something similar, and it might have the time-of-day associated with it, if it was a radio report that came in. The radar fades out rather quickly, but the radio reports will hang around roughly 24 hours.