Very likely mostly capped sugar water with real some real honey mixed in. People usually stop feeding when they add the first super. Save it for winter. Do you have a late flow coming? Give them new frames, stop feeding, and see if you can get a late harvest. Add these sugar frames back for winter.
Edited to add...Yes, I am in Florida, so winter rules don't apply here, but my 76 year young Mom is a 2nd year beek in Mass, and I have been mentoring her, as well. SO though your rules don't apply to me, they do apply to her.