I would say a miscalculation on the due date. I had an US at 7w 1d and my baby looked pretty much like a blurry peanut with a heartbeat. (Was still too soon to hear the heartbeat but could see it.)
Of course the baby is 100% human, i meant more humanlike than other babies around that time. & yeah, maybe my Dr. Miscalculated my due date.
I would suspect a miscalculation of the due date or conception date. Oh, and your baby is 100% human from conception.
All babies develop at different rates. The ultrasound machine could have been a really good one. Its hard so say at this stage.